High-yield method of endohedrally encapsulating species inside fluorinated fullerene nanocages

ABSTRACT

This invention is directed to the fluorination (or derivatization with alternative chemical species) of fullerene carbon nanocages as an efficient way to (a) facilitate synthesis of endohedral complexes by a significant reduction or elimination of the barriers for the entry of guest-ions, -atoms or molecules, and (b) to preserve the chemical stability of final product.

PRIORITY BENEFIT

[0001] This Application is a continuation-in-part of U.S. patentapplication Ser. No. 09/787,473, filed Mar. 16, 2001, which is the 35U.S.C. § 371 national application of International Application No.PCT/US 99/21366, filed Sep. 17, 1999, which designated the UnitedStates, claiming priority to U.S. Patent Application Nos. (1)60/101,092, filed Sep. 18, 1998; (2) 60/106,918 filed Nov. 3, 1998; and(3) 60/138,505, filed Jun. 10, 1999, all of which are herebyincorporated by reference. This Application further claims prioritybenefits to U.S. Patent Application No. 60/427,431.

GOVERNMENT GRANTS

[0002] This invention was made with United States Government supportunder (1) United States Grant No. NAGW-4004 awarded by the NationalAeronautical and Space Administration—Jet Propulsion Laboratory, (2)United States Grant No. DMR-952225 1 awarded by the National ScienceFoundation, and (3) United States Grant No. EED-0118007 (Rice CBEN)awarded by the Nanoscale Science and Engineering Initiative of theNational Science Foundation. The United States Government may havecertain rights in the invention.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] This invention is directed to making chemical derivatives ofcarbon nanotubes and to uses for the derivatized nanotubes, includingmaking arrays as a basis for synthesis of carbon fibers.

[0005] 2. Related Art

[0006] Fullerenes are closed-cage molecules composed entirely ofsp²-hybridized carbons, arranged in hexagons and pentagons. Fullerenes(e., C₆₀) were first identified as closed spheroidal cages produced bycondensation from vaporized carbon.

[0007] Fullerene tubes are produced in carbon deposits on the cathode incarbon arc methods of producing spheroidal fullerenes from vaporizedcarbon. Ebbesen et al. (Ebbesen I), “Large-Scale Synthesis Of CarbonNanotubes,” Nature, Vol. 358, p. 220 (Jul. 16, 1992) and Ebbesen et al.,(Ebbesen II), “Carbon Nanotubes,” Annual Review of Materials Science,Vol. 24, p. 235 (1994). Such tubes are referred to herein as carbonnanotubes. Many of the carbon nanotubes made by these processes weremulti-wall nanotubes, i e., the carbon nanotubes resembled concentriccylinders. Carbon nanotubes having up to seven walls have been describedin the prior art. Ebbesen II; Iijima et al., “Helical Microtubules OfGraphitic Carbon,” Nature, Vol. 354, p. 56 (Nov. 7, 1991).

[0008] Production of Single-Wall Nanotubes

[0009] Single-wall carbon nanotubes (SWNT) have been made in a DC arcdischarge apparatus of the type used in fullerene production bysimultaneously evaporating carbon and a small percentage of VIII Btransition metal from the anode of the arc discharge apparatus. SeeIijima et al., “Single-Shell Carbon Nanotubes of 1 nm Diameter,” Nature,Vol. 363, p. 603 (1993); Bethune et al., “Cobalt Catalyzed Growth ofCarbon Nanotubes with Single Atomic Layer Walls,” Nature, Vol. 63, p.605 (1993); Ajayan et al., “Growth Morphologies During Cobalt CatalyzedSingle-Shell Carbon Nanotube Synthesis,” Chem. Phys. Lett., Vol. 215, p.509 (1993); Zhou et al., “Single-Walled Carbon Nanotubes GrowingRadially From YC₂ Particles,” Appl. Phys. Lett., Vol. 65, p. 1593(1994); Seraphin et al., “Single-Walled Tubes and Encapsulation ofNanocrystals Into Carbon Clusters, “Electrochem. Soc., Vol. 142, p. 290(1995); Saito et al., “Carbon Nanocapsules Encaging Metals andCarbides,” J. Phys. Chem. Solids, Vol. 54, p. 1849 (1993); Saito et al.,“Extrusion of Single-Wall Carbon Nanotubes Via Formation of SmallParticles Condensed Near an Evaporation Source,” Chem. Phys. Lett., Vol.236, p. 419 (1995). It is also known that the use of mixtures of suchtransition metals can significantly enhance the yield of single-wallcarbon nanotubes in the arc discharge apparatus. See Lambert et al.,“Improving Conditions Toward Isolating Single-Shell Carbon Nanotubes,”Chem. Phys. Lett., Vol. 226, p. 364 (1994). While the arc dischargeprocess can produce single-wall nanotubes, the yield of nanotubes is lowand the tubes exhibit significant variations in structure and sizebetween individual tubes in the mixture. Individual carbon nanotubes aredifficult to separate from the other reaction products and purify.

[0010] An improved method of producing single-wall nanotubes isdescribed in U.S. Ser. No. 08/687,665, entitled “Ropes of Single-WalledCarbon Nanotubes” incorporated herein by reference in its entirety. Thismethod uses, inter alia, laser vaporization of a graphite substratedoped with transition metal atoms, preferably nickel, cobalt, or amixture thereof, to produce single-wall carbon nanotubes in yields of atleast 50% of the condensed carbon. The single-wall nanotubes produced bythis method tend to be formed in clusters, termed “ropes,” of 10 to 1000single-wall carbon nanotubes in parallel alignment, held together by vander Waals forces in a closely packed triangular lattice. Nanotubesproduced by this method vary in structure, although one structure tendsto predominate.

[0011] A method of producing carbon fibers from single-wall carbonnanotubes is described in PCT Patent Application No. PCT/US98/04513,incorporated herein by reference in its entirety. The carbon fibers areproduced using SWNT molecules in a substantially two-dimensional arraymade up of single-walled nanotubes aggregated (e.g., by van der Waalsforces) in substantially parallel orientation to form a monolayerextending in directions substantially perpendicular to the orientationof the individual nanotubes. In this process the seed array tubes areopened at the top (free) end and a catalyst cluster is deposited at thisfree end. A gaseous carbon source is then provided to grow the nanotubeassembly into a fiber. In various processes involving metal clustercatalysis, it is important to provide the proper number of metal atomsto give the optimum size cluster for single wall nanotube formation.

[0012] Definition of Terms

[0013] “Fullerene carbon nanocages” is a term which encompassesfullerenes, buckyballs, carbon nanotubes, nested fullerenes, buckyonions, single-wall carbon nanotubes, multi-wall carbon nanotubes, andcarbon fibrils.

[0014] “Endohedrally-doped fullerene carbon nanocages” refers tofullerene carbon nanocages (see above) which have something inside ofthem. That endohedral species can be an atom, a cluster of atoms, or asmall molecule.

[0015] “Derivatized fullerene carbon nanocage” refers to a fullerenecarbon nanocage which has atoms or functional groups (i.e., hydroxyl,methyl, phenyl, nitro, amino, etc.) covalently attached to the exteriorof the fullerene carbon nanocage.

[0016] “Fluorinated fullerene carbon nanocage” refers to a fullerenecarbon nanocage which has fluorine atoms covalently attached to theexterior of the fullerene carbon nanocage. This is a subset of thederivatized fullerene carbon nanocage mentioned above.

[0017] “Endohedral doping agent” refers to the species that is insertedinto the fullerene carbon nanocage (or fluorinated fullerene carbonnanocage, or derivatized fullerene carbon nanocage) to generate anendohedrally-doped fullerene carbon nanocage (or an endohedrally-dopedfluorinated fullerene carbon nanocage, or an endohedrally-dopedderivatized fullerene carbon nanocage).

[0018] Derivatization of Single-Wall Nanotubes

[0019] Since the discovery of single wall carbon nanotubes (SWNTs) in1993 (Iijima, S. and Ichihashi, T., Nature 1993,363:603-605),researchers have been searching for ways to manipulate them chemically.While there have been many reports and review articles on the productionand physical properties of carbon nanotubes, reports on chemicalmanipulation of nanotubes have been slow to emerge. There have beenreports of functionalizing nanotube ends with carboxylic groups (Rao, etal., Chem. Commun., 1996,1525-1526; Wong, et al., Nature,1998,394:52-55), and then further manipulation to tether them to goldparticles via thiol linkages (Liu, et al., Science, 1998,280:1253-1256). Haddon and co-workers (Chen, et al., Science, 1998,282:95-98) have reported solvating SWNTs by adding octadecylamine groupson the ends of the tubes and then adding dichlorocarbenes to thenanotube side wall, albeit in relatively low quantities (˜2%). Whiletheoretical results have suggested that finctionalization of thenanotube side-wall is possible (Cahill, et al., Tetrahedron,1996, 52(14):5247-5256), experimental evidence confirming this theory has notbeen obtained.

[0020] Endohedrally-Doped Fullerene Carbon Nanocages

[0021] Endohedrally-doped fullerene carbon nanocages have captured theimagination of those in the bio-medical community. While the delivery ofradioactive isotopes for biomedical applications (diagnostics andtreatment) to specific targets inside living organisms is currently animportant area of focus (radiopharmaceuticals), there exist manyproblems with regard to the chemical and radioactive instability of thecompounds containing radioactive isotopes, and with the relatively highlevel of toxicity that these compounds possess.

[0022] Problems with the instability and toxicity of suchradiopharmaceuticals can be overcome by encapsulation of the radioactivecomponents into chemically and radioactively stable fullerene carbonnanocages, of which C₆₀ is a prime example. Such nanocages can becovered by surfactants and specific targeting antibodies to make thestructures soluble in water or other solvents and to achieve specificbinding, e.g., to tumor cells. To protect these cage-containers fromchemical destruction, to ensure their solubility and enhancedbiocompatibility, and to facilitate the attachment of bio-specificligands, a surfactant (e.g. Pluronics, a block ABA copolymer ofpoly(oxyethylene) and poly(oxypropylene)) can be used on the cageexterior.

[0023] Perhaps one of the most interesting fullerene carbon nanocagestructures for such abovementioned endeavors are single wall carbonnanotubes (SWNTs), due to their unique dimensions and low-level ofsurface reactivity. While they are difficult to separate due to theirstrong affinity towards each other, surfactants have been shown to aidin their dispersal [A. Rinzler et al. “Large-Scale Purification ofSingle-Wall Carbon Nanotubes: Process, Product, and Characterization,”Applied Physics A, Vol. 67, p. 29 (1998)]. For biomedical targeting, thesurfactant can be labeled with specific antibodies, such as tumorantibodies [K. Gonzalez et al. “Synthesis and In Vitro Characterizationof a Tissue-Selective Fullerene: Vectoring C₆₀(OH)₁₆AMBP to MineralizedBone,” Bioorg. Med. Chem., p. 1991 (2002)].

[0024] At present, there is no efficient way to synthesize fullerenecarbon nanocage endohedral complexes (carbon cage-like molecularstructures containing ions, atoms, or molecules within their interior).The main disadvantage of all currently known methods (high-temperaturesynthesis, irradiation with ion beams, high-pressure treatment of thecarbon cages with gases like H₂, He, etc.) is a very low synthetic yield(generally no more than ˜0.1%). In addition, encapsulation by directirradiation with ion beams often results in the destruction of thecages. This is due to the fact that the ions must possess considerablekinetic energy to overcome the high potential energy barriers associatedwith ion penetration through the cage walls. Transfer of this energy tothe cage can also result in fundamental changes of the chemicalproperties of the structure leading to cage destruction.

[0025] Insertion of uncharged species via treatment with hightemperatures and pressures likely involves the breaking and subsequentreformation of carbon-carbon bonds during the insertion process. Afterinsertion, the cage is thought to close up much like a self-sealingautomobile tire. This process has been described previously [M. Saunderset al. “Noble Gas Atoms Inside Fullerenes,” Science, Vol. 271, p. 1693(1996)] and produced somewhat higher yields (˜2%).

[0026] Direct high-temperature synthesis (arc synthesis using dopedcarbon rods) of such endohedral fullerene carbon nanocage complexes isextremely costly given that yields of the compound are very low (on theorder of 1% or less) [Y. Chai et al. “Fullerenes with Metals Inside,”Journal of Physical Chemistry, Vol. 95, p. 7564 (1991)]. Furthermore,when endohedrally doping the fullerene carbon nanocages with aradioactive species (desired for bio-medical applications), one is facedwith safety and environmental issues surrounding the production ofradioactive pollution. Consequently, a more efficient method ofendohedrally-doping fullerene carbon nanocages would be of greatbenefit.

SUMMARY OF THE INVENTION

[0027] Accordingly, it is an object of this invention to provide amethod for derivatizing carbon nanotubes, especially the side walls ofsingle-wall carbon nanotubes.

[0028] It is another object of this invention to provide a high yield,single step method for producing large quantities of continuousmacroscopic carbon fiber from single-wall carbon nanotubes usinginexpensive carbon feedstocks at moderate temperatures.

[0029] It is yet another object of this invention to provide macroscopiccarbon fiber made by such a method. These and other objects of thisinvention are met by one or more of the following embodiments.

[0030] This invention provides single wall carbon nanotubes and/ortubular carbon molecules derivatized with substituents covalently bondedto carbon atoms of the side wall of the nanotube or molecule. Thesubstituents may in principle be attached on the interior and/orexterior of the nanotube side wall, but the attachment will not bepredominantly on the exterior wall. In particular, the single wallcarbon nanotubes may have substituents selected from fluorine, alkyl andphenyl attached to the side wall. Such single wall carbon nanotubeshaving fluorine covalently bonded to the side wall of the nanotubedemonstrate high electrical resistance.

[0031] This invention also provides a method for derivatizing carbonnanotubes comprising reacting carbon nanotubes with fluorine gas, thefluorine gas preferably being free of HF. Where the carbon nanotubes aremultiple wall nanotubes, and the temperature is at least 500° C., theproduct may be multiple wall carbon nanotubes derivatized with fluorine.Where the carbon nanotubes are single wall nanotubes, and thetemperature is between 250° C. and 500° C., the product is single wallcarbon nanotubes having fluorine covalently bonded to carbon atoms ofthe side wall of the nanotube.

[0032] In one embodiment, this invention also provides a method forpreparing single wall carbon nanotubes having substituents attached tothe side wall of the nanotube by reacting single wall carbon nanotubeswith fluorine gas and recovering fluorine derivatized carbon nanotubes,then reacting fluorine derivatized carbon nanotubes with a nucleophile.Some of the fluorine substituents are replaced by nucleophilicsubstitution. If desired, the remaining fluorine can be completely orpartially eliminated to produce single wall carbon nanotubes havingsubstituents attached to the side wall of the nanotube. The substituentswill, of course, be dependent on the nucleophile, and preferrednucleophiles include alkyl lithium species such as methyl lithium.Alternatively, fluorine may be fully or partially removed from fluorinederivatized carbon nanotubes by reacting the fluorine derivatized carbonnanotubes with various amounts of hydrazine, substituted hydrazine oralkyl amine.

[0033] This invention also provides a process for preparing a suspensionor solution of single wall carbon nanotubes in various solvents fromwhich individual single wall carbon nanotubes may be isolated, theprocess comprising providing a mass of single wall carbon nanotubes thatinclude bundles of fibers held in close association by van der Waalsforces, derivatizing the side walls of the single wall carbon nanotubeswith a plurality of chemical moieties distributed substantiallyuniformly along the length of said single wall carbon nanotube sidewalls, said chemical moieties having chemical and steric propertiessufficient to prevent the reassembly of van der Waals force boundbundles, producing true solutions and recovering the individual,derivatized single wall carbon nanotubes from said solution orsuspension. Preferably, the attached chemical moieties are fluorine toprovide solution in various alcohols, preferably isopropyl alcohol, andvarious R-groups to appropriate to provide solubility in other solventsincluding CHCl₃, Dimethylformamide, etc.

[0034] In another embodiment, a method for forming a macroscopicmolecular array of tubular carbon molecules is disclosed. This methodincludes the steps of providing at least about 10⁶ tubular carbonmolecules of substantially similar length in the range of 50 to 500 nm;introducing a linking moiety onto at least one end of the tubular carbonmolecules; providing a substrate coated with a material to which thelinking moiety will attach; and contacting the tubular carbon moleculescontaining a linking moiety with the substrate.

[0035] The present invention also provides seed materials for growth ofsingle wall carbon nanotubes comprising a plurality of single wallcarbon nanotubes or short tubular molecules having a catalyst precursormoiety covalently bound or physisorbed on the outer surface of thesidewall to provide the optimum metal cluster size under conditions thatresult in migration of the metal moiety to the tube end.

[0036] This invention also provides a seed array for the catalyticproduction of assemblies of single wall carbon nanotubes comprising aplurality of relatively short single wall carbon nanotubes assembled ina generally parallel configuration, and disposed on the side wall ofeach said single wall carbon nanotube a sufficient quantity ofphysisorbed or covalently bonded transition metal catalyst precursormoieties to provide active catalyst metal atom clusters of the propersize to grow single wall carbon nanotubes under conditions that promotethe generation of metal atoms and the migration of said metal atoms tothe free ends of said single wall carbon nanotubes.

[0037] In another embodiment, a method for continuously growing amacroscopic carbon fiber comprising at least about 10⁶ single-wallnanotubes in generally parallel orientation is disclosed. In thismethod, a macroscopic molecular array of at least about 10⁶ tubularcarbon molecules in generally parallel orientation is provided. Thearray is processed to provide a single plane of open-ended nanotubes atan angle generally perpendicular to the axes of parallel tubes in thearray. The open ends of the tubular carbon molecules in the array arethen contacted with a catalytic metal by causing migration of metalatoms released from side wall attached catalyst precursor groups. Agaseous source of carbon is supplied to the end of the array whilelocalized energy is applied to the end of the array in order to heat theend to a temperature in the range of about 500° C. to about 1300° C. Thegrowing carbon fiber is continuously recovered.

[0038] In another embodiment, an apparatus for forming a continuousmacroscopic carbon fiber from a macroscopic molecular template arraysimilar to that described above, comprising at least about 10⁶single-wall carbon nanotubes having a catalytic metal deposited on theopen ends of said nanotubes is disclosed. This apparatus includes ameans for locally heating only the open ends of the nanotubes in thetemplate array in a growth and annealing zone to a temperature in therange of about 500° C. to about 1300° C. It also includes a means forsupplying a carbon-containing feedstock gas to the growth and annealingzone immediately adjacent the heated open ends of the nanotubes in thetemplate array. It also includes a means for continuously removinggrowing carbon fiber from the growth and annealing zone whilemaintaining the growing open end of the fiber in the growth andannealing zone.

[0039] In another embodiment, the present invention is for thefluorination of fullerene carbon nanocages as an efficient way to (a)facilitate synthesis of endohedral complexes by a significant reductionor elimination of the barriers for the entry of guest-ions, -atoms ormolecules, and (b) to preserve the chemical stability of the finalproduct. The fluorination of the fullerene carbon nanocage exteriormakes it easier for low-energy ions or thermally-excited atoms ormolecules to “punch” their way through the nanocage wall.

[0040] The physical cause of these effects is the destruction of thechemically-active π-electron system followed by the formation of new C—Fcovalent bonds. Quantum chemical and molecular dynamics simulations showthat the penetration barrier can be reduced several times (e.g. for H⁺2-6 times, to almost 1.5 eV), depending upon the precise point of entryon the cage surface. This permits the use of low energy ion beams orhigh temperatures and pressures for insertion of radioactive isotopes(e.g. T⁺, T₂, ³He, or for a series of cobalt isotopes of small ionicradius) into the cages. At the same time, the analogous barriers for theexit outside the cage remain high. This ensures that the activecomponent, and the radioactive decay products, are retained within thecage.

[0041] Endohedrally-doping fluorinated fullerene carbon nanocagestructures as described herein will facilitate the generation of aseries of products of general type X@C_(m)F_(n), where where Xrepresents one or more endohedral doping species, that can be producedin industrial quantities. Such products will serve as nanoscale sourcesof radiation of different types (neutron, γ-rays, β-rays, α-particles,etc.) for medical diagnostics, materials science, and in the productionof other high-technology products.

[0042] While fluorination is the prime candidate for facilitating theendohedral-doping of fullerene carbon nanocages, it is plausible thatfullerene carbon nanocages derivatized with species other than fluorinecould effect the same or similar results.

[0043] The foregoing objectives, and others apparent to those skilled inthe art, are achieved according to the present invention as describedand claimed herein, and in the text of U.S. provisional application No.60/106,918, filed Nov. 3, 1998, which is incorporated herein in itsentirety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044]FIG. 1. A) TEM image of pure, unreacted SWNT B) TEM of SWNT afterbeing fluorinated at 325° C. C) TEM of SWNT after being fluorinated at500° C. D) another TEM of SWNT fluorinated at 500° C. showing theformation of MWNT.

[0045]FIG. 2. Raman spectrum of pure, unreacted carbon SWNT.

[0046]FIG. 3. Raman spectra of SWNT fluorinated at A) 250° C. B) 325° C.and C) 400° C.

[0047]FIG. 4. Raman spectra showing the defluorination of the nanotubesoriginally fluorinated at A) 250° C. B) 325° C. and C) 400° C.

[0048]FIG. 5. A) SEM of pure, unreacted SWNT B) SEM of SWNT after havingbeen fluorinated at 325° C. for 5 hours C) SEM of SWNT fluorinated at325° C. and then defluorinated in hydrazine.

[0049]FIG. 6. A) Raman spectrum of SWNT after being fluorinated and thenmethylated. B) Raman spectrum of the pyrolyzed methylated. SWNT whichlooks exactly like the Raman spectrum of untreated SWNT.

[0050]FIG. 7. B) EI mass spectrum of products given off during thepyrolysis of methylated SWNT. This spectrum corresponds to a probetemperature of ˜400° C.

[0051]FIG. 8. A) Infrared spectrum of the product of a 3 hourmethylation reaction B) Infrared spectrum. of the product of a 12 hourmethylation reaction.

[0052]FIG. 9 shows a SEM image of purified SWNTs.

[0053]FIG. 10A shows an AFM image of fluorotubes which have beendissolved in 2-butanol and dispersed on inica.

[0054]FIG. 10B shows a typical height analysis of the scan in FIG. 2A,revealing the tube diameters to be on the order of 1.2-1.4 nm, values onthe order of those determined previously for this product using TEM andXRD.

[0055]FIG. 11 shows a UV spectrum of fluorotubes solvated in 2-propanolafter sonication times of A) 10 min. B) 40 min. and C) 130min.

[0056]FIG. 12A shows an AFM image of fluorotubes after having beendefluorinated with N₂H₄, filtered, resuspended in DMF and dispersed onmica.

[0057]FIG. 12B shows an AFM image of untreated SWNTs dispersed on mica.

[0058]FIG. 13A shows a Raman spectrum of pure, untreated SWNTs.

[0059]FIG. 13B shows a Raman spectrum of fluorotubes.

[0060]FIG. 13C shows a Raman spectrum of fluorotubes after having beendefluorinated with N₂H₄. * denotes Ar plasma line.

[0061]FIG. 14 is a schematic representation of a portion of anhomogeneous SWNT molecular array according to the present invention.

[0062]FIG. 15 is a schematic representation of an heterogeneous SWNTmolecular array according to the present invention.

[0063]FIG. 16 is a schematic representation of the growth chamber of thefiber apparatus according to the present invention.

[0064]FIG. 17 is a schematic representation of the pressure equalizationand collection zone of the fiber apparatus according to the presentinvention.

[0065]FIG. 18 is a composite array according to the present invention.

[0066]FIG. 19 is a composite array according to the present invention.

[0067]FIG. 20 is illustrates (a) the energy barrier for inserting a H⁺ion into C₆₀, and (b) how this energy barrier is lowered by addingfluorines.

[0068]FIG. 21 is a density of states plot illustrating how the electrondensity changes upon covalently adding fluorine to the exterior of C₆₀.

[0069]FIG. 22 illustrates how surfactants and antibodies can be attachedto the endohedrally-doped fullerene carbon nanocage for targeteddelivery in pharmaceutical applications.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0070] Carbon has from its very essence not only the propensity toself-assemble from a high temperature vapor to form perfect spheroidalclosed cages (of which C₆₀ is prototypical), but also (with the aid of atransition metal catalyst) to assemble into perfect single-wallcylindrical tubes which may be sealed perfectly at both ends with asemifullerene dome. These tubes, which may be thought of asone-dimensional single crystals of carbon, are true fullerene molecules.

[0071] Single-wall carbon nanotubes are much more likely to be free ofdefects than multi-wall carbon nanotubes. Defects in single-wall carbonnanotubes are less likely than defects in multi-walled carbon nanotubesbecause the latter have neighboring walls that provide for easily-formeddefect sites via bridges between unsaturated carbon valances in adjacenttube walls. Since single-wall carbon nanotubes have fewer defects, theyare stronger, more conductive, and therefore more useful than multi-wallcarbon nanotubes of similar diameter.

[0072] Carbon nanotubes, and in particular the single-wall carbonnanotubes, are useful for making electrical connectors in micro devicessuch as integrated circuits or in semiconductor chips used in computersbecause of the electrical conductivity and small size of the carbonnanotube. The carbon nanotubes are useful as antennas at opticalfrequencies, and as probes for scanning probe microscopy such as areused in scanning tunneling microscopes (STM) and atomic forcemicroscopes (AFM). The carbon nanotubes may be used in place of or inconjunction with carbon black in tires for motor vehicles. The carbonnanotubes are also useful as supports for catalysts used in industrialand chemical processes such as hydrogenation, reforming and crackingcatalysts.

[0073] Ropes of single-wall carbon nanotubes will conduct electricalcharges with a relatively low resistance. Ropes are useful in anyapplication where an electrical conductor is needed, for example as anadditive in electrically conductive paints or in polymer coatings or asthe probing tip of an STM.

[0074] In defining carbon nanotubes, it is helpful to use a recognizedsystem of nomenclature. In this application, the carbon nanotubenomenclature described by M. S. Dresselhaus, G. Dresselhaus, and P. C.Eklund, Science of Fullerness and Carbon Nanotubes, Chap. 19, especiallypp. 756-760, (1996), published by Academic Press, 525 B Street, Suite1900, San Diego, Calif. 92101-4495 or 6277 Sea Harbor Drive, Orlando,Fla. 32877 (ISBN 0-12-221820-5), which is hereby incorporated byreference, will be used. The single wall tubular fullerenes aredistinguished from each other by double index (n,m) where n and m areintegers that describe how to cut a single strip of hexagonal“chicken-wire” graphite so that it makes the tube perfectly when it iswrapped onto the surface of a cylinder and the edges are sealedtogether. When the two indices are the same, m=n, the resultant tube issaid to be of the “arm-chair” (or n,n) type, since when the tube is cutperpendicular to the tube axis, only the sides of the hexagons areexposed and their pattern around the periphery of the tube edgeresembles the arm and seat of an arm chair repeated n times. Arm-chairtubes are a preferred form of single-wall carbon nanotubes since theyare metallic, and have extremely high electrical and thermalconductivity. In addition, all single-wall nanotubes have extremely hightensile strength.

[0075] Carbon nanotubes may have diameters ranging from about 0.6nanometers (nm) for a single-wall carbon nanotube up to 3 nm, 5 nm, 10nm, 30 nm, 60 nm or 100 nm for single-wall or multi-wall carbonnanotubes. The carbon nanotubes may range in length from 50 nm up to 1millimeter (mm), 1 centimeter (cm), 3 cm, 5 cm, or greater. The yield ofsingle-wall carbon nanotubes in the product made by this invention isunusually high.

[0076] Catalytic Formation of Carbon Nanotubes

[0077] As will be described further, one or more transition metals ofGroup VIB chromium (Cr), molybdenum (Mo), tungsten (W) or Group VIII Btransition metals, e.g., iron (Fe), cobalt (Co), nickel (Ni), ruthenium(Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir) andplatinum (Pt) catalyze the growth of a carbon nanotube and/or ropes whencontacted with a carbon bearing gas such carbon monoxide andhydrocarbons, including aromatic hydrocarbons, e.g., benzene, toluene,xylene, cumene, ethylbenzene, naphthalene, phenanthrene, anthracene ormixtures thereof, non-aromic hydrocarbons, e.g., methane, ethane,propane, ethylene, propylene, acetylene or mixtures thereof; andoxygen-containing hydrocarbons, e.g., formaldehyde, acetaldehyde,acetone, methanol, ethanol or mixtures thereof. Mixtures of one or moreGroup VIB or VIIIB transition metals also selectively producesingle-wall carbon nanotubes and ropes of single-wall carbon nanotubesin higher yields. The mechanism by which the growth in the carbonnanotube and/or rope is accomplished is not completely understood.However, it appears that the presence of the one or more Group VI B orVIII B transition metals on the end of the carbon nanotube facilitatesthe addition of carbon from the carbon vapor to the solid structure thatforms the carbon nanotube. Applicants believe this mechanism isresponsible for the high yield and selectivity of single-wall carbonnanotubes and/or ropes in the product and will describe the inventionutilizing this mechanism as merely an explanation of the results of theinvention. Even if the mechanism is proved partially or whollyincorrect, the invention which achieves these results is still fullydescribed herein.

[0078] One aspect of the invention comprises a method of making carbonnanotubes and/or ropes of carbon nanotubes which comprises supplyingcarbon vapor to the live end of one or more of a carbon nanotubesgrowing by a catalytic process in which there is a “live end” of thenanotube in contact with a nanometer-scale transition metal particlethat serves as a catalyst. The live end of the nanotube is maintained incontact with a carbon bearing feedstock gas in an annealing zone at anelevated temperature. In one process of this type carbon in vapor formmay be supplied in accordance with this invention by an apparatus inwhich a laser beam impinges on a target comprising carbon that ismaintained in a heated zone. A similar apparatus has been described inthe literature, for example, in U.S. Pat. No. 5,300,203, or inPCT/US96/14188, both of which are incorporated herein by reference, andin Chai, et al., “Fullerenes with Metals Inside,” J. Phys. Chem., vol.95, no. 20, p. 7564 (1991). Alternatively carbon may be added to thelive end by the direct action of the catalytic particle in the annealingzone with a carbon-bearing feedstock gas such as carbon monoxide andhydrocarbons, including aromatic hydrocarbons, e.g., benzene, toluene,xylene, cumene, ethylbenzene, naphthalene, phenanthrene, anthracene ormixtures thereof, non-aromic hydrocarbons, e.g., methane, ethane,propane, ethylene, propylene, acetylene or mixtures thereof; andoxygen-containing hydrocarbons, e.g., formaldehyde, acetaldehyde,acetone, methanol, ethanol or mixtures thereof.

[0079] According to this invention, a “live end” can also be produced ona carbon nanotube derivatized with chemical moieties which bind Group VIB or Group VIII B metal to the tube. This mode is discussed in greaterdetail below. Additional carbon vapor is then supplied to the live endof a carbon nanotube under the appropriate conditions to increase thelength of the carbon nanotube.

[0080] The carbon nanotube that is formed is not always a single-wallcarbon nanotube; it may be a multi-wall carbon nanotube having two,five, ten or any greater number of walls (concentric carbon nanotubes).Preferably, though, the carbon nanotube is a single-wall carbonnanotube, and this invention provides a way of selectively producingsingle-wall carbon nanotubes in greater and sometimes far greaterabundance than multi-wall carbon nanotubes.

[0081] Elongation of Single-Wall Nanotubes

[0082] As contemplated by this invention, growth or elongation ofsingle-wall carbon nanotubes requires that carbon in vapor form besupplied to the live end of the growing nanotube in an annealing zone.In this application, the term “live end” of a carbon nanotube refers tothe end of the carbon nanotube on which catalytic amounts of one or moreGroup VI B or VIII B transition metals are located. The catalyst shouldbe present on the open SWNT ends as a metal cluster containing fromabout 10 metal atoms up to about 200 metal atoms (depending on the SWNTmolecule diameter). Preferred are metal clusters having a cross-sectionequal to from about 0.5 to about 1.0 times the tube diameter (e.g.,about 0.7 to 1.5 nm).

[0083] A carbon nanotube having a live end will grow in length by thecatalytic addition of carbon from the vapor to the live end of thecarbon nanotube if the live end is placed in an annealing zone and thenadditional carbon-containing vapor is supplied to the live end of thecarbon nanotube. The annealing zone where the live end of the carbonnanotube is initially formed should be maintained at a temperature of500° to 1500° C., more preferably 1000° to 1400° C. and most preferably1100 to 1300° C. In embodiments of this invention where carbon nanotubeshaving live ends are caught and maintained in an annealing zone andgrown in length by further addition of carbon (without the necessity ofadding further Group VI B or VIII B transition metal vapor), theannealing zone may be cooler, 400° to 1500° C., preferably 400° to 1200°C., most preferably 500° to 700° C. The pressure in the annealing zoneshould be maintained in the range of pressure appropriate to thecatalyst/feedstock system being used, i.e., 50 to 2000 Torr, morepreferably 100 to 800 Torr, and most preferably 300 to 600 Torr in thecase of carbon or hydrocarbon gasses, but up to 100 atmospheres in thecase of CO feedstock. The atmosphere in the annealing zone will containcarbon in some form. Normally, the atmosphere in the annealing zone willalso comprise a gas that sweeps the carbon vapor through the annealingzone to a collection zone. Any gas that does not prevent the formationof carbon nanotubes will work as the sweep gas, but preferably the sweepgas is an inert gas such as helium, neon, argon, krypton, xenon, ormixtures of two or more of these. Helium and Argon are most preferred.The use of a flowing inert gas provides the ability to controltemperature, and more importantly, provides the ability to transportcarbon to the live end of the carbon nanotube. In some embodiments ofthe invention, when other materials are being vaporized along withcarbon, for example one or more Group VI B or VIII B transition metals,those compounds and vapors of those compounds will also be present inthe atmosphere of the annealing zone. If a pure metal is used, theresulting vapor will comprise the metal. If a metal oxide is used, theresulting vapor will comprise the metal and ions or molecules of oxygen.

[0084] It is important to avoid the presence of too many materials thatkill or significantly decrease the catalytic activity of the one or moreGroup VI B or VIII B transition metals at the live end of the carbonnanotube. It is known that the presence of too much water (H₂0) and/oroxygen (O₂) will kill or significantly decrease the catalytic activityof the one or more Group VI B or VIII B transition metals. Therefore,water and oxygen are preferably excluded from the atmosphere in theannealing zone. Ordinarily, the use of a sweep gas having less than 5 wt%, more preferably less than 1 wt % water and oxygen will be sufficient.Most preferably the water and oxygen will be less than 0.1 wt %.

[0085] The carbon-containing vapor supplied to the live end in theannealing zone may be provided by evaporation of a solid carbon targetusing energy supplied by an electric arc or laser, as described herein.However, once the single-wall carbon nanotube having a live end isformed, the live end will catalyze growth of the single-wall carbonnanotube at lower temperatures and with other carbon sources. Analternative carbon source for growing the SWNT may be fullerenes, thatcan be transported to the live end by the flowing sweep gas. The carbonsource can be graphite particles carried to the live end by the sweepgas. The carbon source can be a hydrocarbon that is carried to the liveend by a sweep gas or a hydrocarbon gas or mixture of hydrocarbon gassesintroduced into the annealing zone. Hydrocarbons useful include methane,ethane, propane, butane, ethylene, propylene, benzene, toluene or anyother paraffinic, olefinic, cyclic or aromatic hydrocarbon, or any otherhydrocarbon. Another alternative that may be used as a source ofcarbon-containing vapor are other gaseous compounds that can formelemental carbon by disproportionation such as CO, C₂F₄ and C₂H₄.

[0086] Chemically Modified Carbon Nanotubes

[0087] The present invention provides carbon nanotubes having chemicallyderivatized side walls. In preferred embodiments, the derivatizationfacilitates formation of more complex functional compounds with carbonnanotubes. Derivatization also enables complexing of Group VI B and/orGroup VIII B metals on the nanotubes. In particularly preferredembodiments, the derivatized nanotubes are derivatized molecular growthprecursors of this invention which may have the following structures andfunctions:

[0088] where

[0089] is a substantially defect-free cylindrical graphene sheet (whichoptionally can be doped with non-carbon atoms) having from about 10² toabout 10⁷ carbon atoms, and having a length of from about 5 to about10000 nm, preferably about 5 to about 500 nm;

[0090] is a fullerene cap that fits perfectly on the cylindricalgraphene sheet, has at least six pentagons and the remainder hexagonsand typically has at least about 30 carbon atoms;

[0091] M is a Group VI B or VIII B metal

[0092] n Is a number from 10-100000, preferably 50 to 20000; and

[0093] R is a linking or complexing moiety that can include groupsselected from the group consisting of alkyl, acyl, aryl, aralkyl,halogen; substituted or unsubstituted thiol; unsubstituted orsubstituted amino; hydroxy, and OR′ wherein R′ is selected from thegroup consisting of hydrogen, alkyl, acyl, aryl aralkyl, unsubstitutedor substituted amino; substituted or unsubstituted thiol; and halogen;and a linear or cyclic carbon chain optionally interrupted with one ormore heteroatom, and optionally substituted with one or more ═O, or ═S,hydroxy, an aminoalkyl group, an amino acid, or a peptide of 2-8 aminoacids.

[0094] Other embodiments of the derivatized nanotubes of this inventionhave structures as described above, except metal is not present and theR group does not necessarily serve to form complexes. The followingdefinitions are used herein.

[0095] The term “alkyl” as employed herein includes both straight andbranched chain radicals, for example methyl, ethyl, propyl, isopropyl,butyl, t-butyl, isobutyl, pentyl, hexyl, isohexyl, heptyl,4,4-dimethylpentyl, octyl, 2,2,4-trimethylpentyl, nonyl, decyl, undecyl,dodecyl, the various branched chain isomers thereof. The chain may belinear or cyclic, saturated or unsaturated, containing, for example,double and triple bonds. The alkyl chain may be interrupted orsubstituted with, for example, one or more halogen, oxygen, hydroxy,silyl, amino, or other acceptable substituents.

[0096] The term “acyl” as used herein refers to carbonyl groups of theformula —COR wherein R may be any suitable substituent such as, forexample, alkyl, aryl, aralkyl, halogen; substituted or unsubstitutedthiol; unsubstituted or substituted amino, unsubstituted or substitutedoxygen, hydroxy, or hydrogen.

[0097] The term “aryl” as employed herein refers to monocyclic, bicyclicor tricyclic aromatic groups containing from 6 to 14 carbons in the ringportion, such as phenyl, naphthyl, substituted phenyl, or substitutednaphthyl, wherein the substituent on either the phenyl or naphthyl maybe for example C₁₋₄ alkyl, halogen, C₁₋₄ alkoxy, hydroxy or nitro.

[0098] The term “aralkyl” as used herein refers to alkyl groups asdiscussed above having an aryl substituent, such as benzyl,p-nitrobenzyl, phenylethyl, diphenylmethyl, and triphenylmethyl.

[0099] The term “aromatic or non-aromatic ring” as used herein includes5-8 membered aromatic and non-aromatic rings uninterrupted orinterrupted with one or more heteroatom, for example O, S, SO, SO₂, andN, or the ring may be unsubstituted or substituted with, for example,halogen, alkyl, acyl, hydroxy, aryl, and amino, said heteroatom andsubstituent may also be substituted with, for example, alkyl, acyl,aryl, or aralkyl.

[0100] The term “linear or cyclic” when used herein includes, forexample, a linear chain which may optionally be interrupted by anaromatic or non-aromatic ring. Cyclic chain includes, for example, anaromatic or non-aromatic ring which may be connected to, for example, acarbon chain which either precedes or follows the ring.

[0101] The term “substituted amino” as used herein refers to an aminowhich may be substituted with one or more substituent, for example,alkyl, acyl, aryl, aralkyl, hydroxy, and hydrogen.

[0102] The term “substituted thiol” as used herein refers to a thiolwhich may be substituted with one or more substituent, for example,alkyl, acyl, aryl, aralkyl, hydroxy, and hydrogen.

[0103] Typically, open ends may contain up to about 20 substituents andclosed ends may contain up to about 30 substituents. It is preferred,due to stearic hindrance, to employ up to about 12 substituents per end.

[0104] In addition to the above described external derivatization, theSWNT molecules of the present invention can be modified endohedrally, ie., by including one or more other atoms or molecules inside thestructure, as is known in the endohedral fullerene art.

[0105] To produce endohedral tubular carbon molecules, the internalspecies (e.g., metal atom) can either be introduced during the SWNTformation process or added after preparation of the nanotubes.

[0106] Endohedrally loaded tubular carbon molecules can then beseparated from empty tubes and any remaining loading materials by takingadvantage of the new properties introduced into the loaded tubularmolecules, for example, where the metal atom imparts magnetic orparamagnetic properties to the tubes, or the bucky ball imparts extramass to the tubes. Separation and purification methods based on theseproperties and others will be readily apparent to those skilled in theart.

[0107] Derivatization of SWNT Sidewalls with Fluorine

[0108] Since the discovery of single wall carbon nanotubes (SWNT)Iijima, et al. (1993), there has been a flurry of research activityaimed at understanding their physical properties (Issi, et al. (1995),Carbon, 33:941-948), elucidating their growth mechanisms (Cornwell, etal. (1997), Chem. Phys. Lett., 278:262-266), and developing novel usesfor them (Dillon, et al. (1997), Nature, 386:377-389). Chemistryinvolving SWNT is still in its infancy. This is due, in large part, toprevious difficulties in obtaining reasonable quantities of highlypurified SWNT.

[0109] Progress in the bulk synthesis and purification (Rinzler, et al.,1998, App. Phys. A, 67:29-37) of SWNT is now making available highquality samples in sufficient quantities to begin exploring the chemicalmodification of this fascinating class of materials. Recently,sono-chemistry was employed to cut the long, intertangled tubes intoindependent, macro-molecular scale, open tube fragments (50-300 nm long)(Liu, et al., 1998). In that work, the high reactivity of the danglingcarbon bonds at the open tube ends was exploited to tether the tubes togold particles via thiol linkages.

[0110] In contrast to the open tube ends, the side-walls of the SWNT, byvirtue of their aromatic nature, possess a chemical stability akin tothat of the basal plane of graphite (Aihara, 1994, J. Phys. Chem.,98:9773-9776). The chemistry available for modification of the nanotubeside-wall (without disruption of the tubular structure) is thussignificantly more restrictive. However, the present inventors haveadapted technology developed in the fluorination of graphite (see, e.g.,Lagow, et al., 1974, J. Chem. Soc., Dalton Trans., 12:1268-1273) to thechemical manipulation of the SWNT side-wall by fluorinating high puritySWNT and then defluorinating them. Once fluorinated, single-wall carbonnanotubes can serve a staging point for a wide variety of side-wallchemical functionalizations, in a manner similar to that observed forfluorinated fullerenes (see Taylor, et al., 1992, J. Chem. Soc., Chem.Comm., 9:665-667, incorporated herein by reference).

[0111] According to the present invention, single-wall carbon nanotubesare derivatized by exposure to a fluorinating agent, which may befluorine gas or any other well known fluorinating agent such as XeF₂,XeF₄, CIF₃, BrF₃, or IF₅. XeF₂, and XeF₄ may be advantageous, being freeof HF. Alternatively, solid fluorinating agents, such as AgF₂ or MnF₃,may be reacted in slurry with SWNT.

[0112] Purified single wall carbon nanotubes (SWNT) were fluorinated bythe inventors by treatment with F₂ at several different temperatures andconcentrations using various mixtures of about 5% F₂ in a one-atmospherepressure mixture with rare gases, including He and Ar. The reactortemperature was between 150° C. and 400° C. Infrared spectroscopy wasused to verify the existence of covalent carbon-fluorine bonds. Productstoichiometries were determined and transmission electron microscopy(TEM) was used to verify whether or not the fluorination was destructiveof the tubes. SWNT fluorinated at three different temperatures were thendefluorinated using hydrazine. Raman spectroscopy was used to verifywhether or not the products of the defluorination were in fact SWNT. Itwas determined, via scanning electron microscopy (SEM) and two-pointresistance measurements, that the bulk of the SWNT survive thefluorination process at temperatures up to 325° C. and that the fluorinecan be effectively removed from the tubes with hydrazine to regeneratethe unfluorinated starting material.

[0113] Not unexpectedly, the electronic properties of the fluorinatedtubes differ dramatically from those of their unfluorinatedcounterparts. While the untreated SWNT are good conductors (10-15Ω twoprobe resistance across the length of the ˜10×3 mm×30 μm bucky papersamples), the tubes fluorinated at temperatures of 250° C. and above areinsulators (two probe resistance>20 MΩ).

[0114] Gravimetric and electron microprobe analysis demonstrated thatlarge amounts of fluorine can be added to SWNT. Resistance measurementsalong with vibrational spectroscopy (Raman, IR) confirm the formation ofnew chemical bonds to the nanotube superstructure. Contributions ofabsorbed molecular fluorine to the overall fluorine uptake are precludedat these temperatures (Watanabe, et al., 1988). It may be concluded,therefore, that fluorine is being covalently attached to the side wallof the SWNT.

[0115] TEM studies have shown that at fluorination temperatures as highas 325° C., the majority of the fluorination product maintains atube-like structure. These studies also indicate that at 500° C., thesingle wall tubular structure does not survive the fluorination processand that some MWNT-like structures are being formed.

[0116] From the product stoichiometries, resistance measurements and IRspectra it is clear that reaction temperatures in excess of 150° C.allow one to covalently add significant amounts of fluorine to the tubewall. The small amount of fluorine that does show up in the product ofthe 150° C. fluorination reaction could be attributed to a combinationof absorbed fluorine and fluorination of the end caps of the SWNT.

[0117] Fluoride can also be effectively removed from the SWNT usinganhydrous hydrazine and that the rejuvenated product is in fact a SWNT.The inventors have found that, once fluorinated, SWNT can bedefluorinated with anhydrous hydrazine via the following reaction:CF_(n)+(n/4)N₂H₄→C+nHF+(n/4)N₂. From the results of these defluorinationexperiments and the Raman and SEM studies associated with them, itappears that a majority of the tubes are destroyed at fluorinationtemperatures of above 400° C., whereas only a slight amount of tubedestruction occurs at 250° C.

[0118] For reactions in which only the outside of the tube is beingfluorinated (the SWNT used in this study were closed at the ends), thereis a limiting stoichiometry of C₂F for which the fluorinated tube canstill maintain its tube-like (albeit puckered) structure. This issupported by the product stoichiometries obtained via elemental analysisand the evidence of significant tube destruction at fluorinationtemperatures greater than 325° C. Further addition of fluorine wouldthen lead to the breaking of carbon-carbon bonds and, hence, destructionof the tube. Accordingly, this invention provides a method ofderivatizing SWNT with F₂ to add fluorine substituents to the exteriorof the sidewalls in stoichiometries of up to C₂F, although lesseramounts of fluorine can also be attached by further diluting thefluorine or by lowering the reaction temperature.

[0119] Changing the Derivatization of SWNT by Fluorine Substitution

[0120] Because the inertness of the SWNT side wall approximates that ofthe basal plane of graphite, chemistry involving the SWNT side wall maybe quite limited. However, the present invention provides methods forfluorination of single wall carbon nanotubes (SWNT) where fluorine iscovalently bound to the side wall of the nanotube and thus provide sitesfor chemical reactions to occur. Functionalization via a fluorinatedprecursor may thus provide an attractive route to a wide range of sidewall derivatizations.

[0121] In a particular embodiment, highly purified single wall carbonnanotubes (SWNTs) may be fluorinated to form “fluorotubes” which canthen be solvated as individual tubes. For example, fluorotubes may besolvated in various alcohol solvents via ultrasonication. The solvationof individual fluorotubes has been verified by dispersing the solvatedtubes on a mica substrate and examining them with atomic forcemicroscopy (AFM). Elemental analysis of the tubes reveals that lightsonication in alcohol solvents does not remove significant amounts ofthe fluorine. These solutions will persist long enough (over a week) topermit solution phase chemistry to be carried out on the fluorotubes.For example, the solvated fluorotubes can be treated with hydrazine toremove fluorine, leading to precipitation from solution of normal,unfluorinated SWNTs. Alternatively, fluorotubes can be reacted withsodium methoxide to yield methoxylated SWNTs. These reaction productshave also been characterized by elemental analysis and a variety ofspectroscopies and microscopies.

[0122] The present inventors have, for the first time, functionalizedthe sidewalls of SWNTs by reacting them with elemental fluorine. Theinventors have discovered that fluorine could be added to the side wallof carbon nanotubes yielding stoichiometries up to approximately C₂Fwithout destruction of the tube-like structure. The inventors have alsodiscovered that a high degree of solvation can be achieved by sonicatingfluorinated SWNTs in a variety of alcohol solvents such as methanol,ethanol, and isopropanol. As demonstrated herein, reactions can becarried out on these nanotubes while in solution by reacting them withhydrazine which serves as a defluorinating agent. It has also beendemonstrated that these “fluorotubes” can be reacted with sodiummethoxide (a strong nucleophile) while in solution to form methoxylatedSWNTs.

[0123] The inventors have shown that single wall carbon nanotubes can befluorinated and then sonicated in alcohols to form stable solutions offluorotubes. This solvation allows one to manipulate the fluorotubes inways that were previously unavailable and opens the door to a widevariety of possibilities with respect to exploring the physical andchemical properties of fluorotubes. “Tuning” the fluorine content of afluorotube by first fluorinating it heterogeneously, solvating it in analcohol, and then defluorinating it with substoichiometric quantities ofhydrazine is consequently available as a way of making a wide varietyfluorotubes with differing fluorine contents and in some instances quitedifferent properties.

[0124] The inventors have further demonstrated that once solvated, thesefluorotubes can then be reacted with species while in solution to eitherdefluorinate or further functionalize them. The chemistry possible withthese solvated fluorotubes provides an important route to the synthesisof a wide variety of functionalized nanotubes having many different anduseful properties.

[0125] An exemplary derivatization is the methylation of SWNT.Methylated SWNT are the product of the nucleophilic substitution offluorine (attached to the SWNT side wall) by the methyl groups in methyllithium. Nucleophilic substitution of this type has been previouslyreported for the reaction between fluorinated C₆₀ and alkyl lithiumspecies (Taylor, et al., 1992). The C—F bonds in fullerene cages andtubes are weakened relative to C—F bonds in alkyl fluorides by aneclipsing strain effect (Taylor, 1998 Russian Chem. Bull., 47:823-832).This renders the bonds more susceptible to nucleophilic attack. A normalS_(N)2 process is geometrically impossible and a S_(N)I process would beextremely unlikely, so either a novel front side displacement orpossibly an addition-elimination process is responsible for thenucleophilic substitution (See Taylor, 1995, in “The Chemistry ofFullerenes,” R. Taylor, ed., World Scientific Publishing, London, pp.208-209).

EXAMPLES

[0126] The following examples are included to demonstrate preferredembodiments of the invention. It should be appreciated by those of skillin the art that the techniques disclosed in the examples which followrepresent techniques discovered by the inventor to function well in thepractice of the invention, and thus can be considered to constitutepreferred modes for its practice. However, those of skill in the artshould, in light of the present disclosure, appreciate that many changescan be made in the specific embodiments which are disclosed and stillobtain a like or similar result without departing from the spirit andscope of the invention.

Example 1

[0127] 1.1 Fluorination of Single-wall Carbon Nanotubes

[0128] Single-walled carbon nanotubes were produced by the dual pulsedlaser vaporization of Co/Ni doped graphite rods and purified bytechniques described previously (Rinzler, et al., 1998). Thepurification product is a metastable colloidal suspension of SWNT“ropes”’ (bundles of hexagonally close packed tubes ranging from a fewto 200 SWNT, See Thess, et al., 1996) in a 0.2% aqueous solution ofTriton X-100 surfactant. Filtering the solution through a PTFE filtermembrane and washing with methanol to remove residual surfactant leavesa black film on the surface. If this layer is sufficiently thick (10-75μm) it can be peeled off to form a free standing film or “bucky paper”of SWNT. This form has appreciable mechanical integrity and isconvenient for handling, and for electrical conductivity and Ramanscattering measurements. It is the fluorination of this “bucky paper”that is described here.

[0129] In fluorinating the SWNT, elemental fluorine (Air Products, 98%)was used as the fluorinating agent. HF, being the major impurity in thefluorine, was removed by passing it through an HF trap (Matheson GasProducts) containing sodium fluoride pellets. The fluorine, diluted withhelium (Trigas, 99.995%), was then passed through atemperature-controlled Monel flow reactor containing the SWNT sample.

[0130] Prior to fluorination, the purified “bucky paper” was vacuumbaked at 1100° C. (2×10⁻⁶ Torr) for several hours in order to desorb anyresidual surface contaminants. For each reaction a pre-weighed piece of“bucky paper” (weighing 150-200 μg) was used. F₂ and He flow rates foreach reaction were 2 sccm and 20 sccm, respectively. In each case thereaction time was 5 hours. The only variable was reaction temperature.As the kinetics of inorganic carbon+fluorine reactions are highlytemperature dependent (Watanabe, et al., 1988, “Graphite fluorides,”Elsevier, Amsterdam), several reactions were carried out at thefollowing temperatures: 150° C., 250° C., 325° C., 400° C., 500° C. and600° C. At reaction temperatures of 325° C. and 400° C., thefluorination was begun at 250° C. and after one hour, the F₂ flow wasstopped and the reactor temperature brought up to the appropriate levelfor an additional 4 hours. For the reactions at 500° C. and 600° C., thesample was fluorinated for 1 hour at 250° C., 1 hour at 400° C. and then3 hours at the specified reaction temperature. The rationale behind this“stepped reaction temperature procedure” was to minimize, as much aspossible, the decomposition: CF₄, CZF₄; C₂F₆, etc. which has been welldocumented in the fluorination of graphite (Kamarchik, et al., 1978,Acc. Chem. Res., 11:196-300) and fullerenes (Selig, et al., 1991, J. Am.Chem. Soc., 113:5475-5476).

[0131] Product stoichiometries as a function of reaction temperaturewere obtained both gravimetrically (TA Instruments TGA-DTA 2960microbalance) and via electron microprobe analysis (Cameca SX 50).Infared spectroscopy (Perkin-Elmer Paragon 1000 FT-IR) was used toconfirm the presence of covalently bound fluorine. Transmission electronmicroscopy (JEOL model 2010 TEM using 100 keV beam energy) was used todetermine if, and at what temperature the tubes were being destroyed(i.e., “unzipped”) by the fluorination. Raman spectroscopy (JobinYvon-Spex model HR460 monochrometer coupled with an ISA Spectrum ONEseries CCD detector and using a 532 nm Nd:YAG laser excitation source),scanning electron microscopy (JEOL model JSM-6320F field emission SEMusing 5 keV beam energy) and two-point resistivity measurements wereused to analyze the untreated, fluorinated and defluorinated SWNTsamples.

[0132] Infared spectroscopy (KBr pellet method) confirmed the presenceof covalently bound fluorine (peaks in the 1220-12.50 cm⁻¹ region) inthe samples fluorinated, at temperatures of 250° C. and higher. No C—Fstretching frequency was seen for the sample fluorinated at 150° C. andits two-point resistance (5 mm apart) was ˜100 which therefore precludeslarge amounts of fluorine being covalently bound to the SWNT side wall.Product stoichiometries of the fluorination reactions are shown inTable 1. Discrepancies between the gravimetric and microprobe analysescan be attributed to product decomposition as described above,especially at the higher temperatures.

[0133]FIG. 1-A shows a TEM image of the purified, unreacted SWNTmaterial.

[0134]FIG. 1-B shows a TEM image of SWNT fluorinated at 325° C. As canbe seen from the image, the tubes remain largely intact after treatmentunder these conditions. FIG. 1-C is a TEM image of SWNT fluorinated at500° C. Here it would appear that the tubes are essentially alldestroyed. However, a fair number of nested tube-like graphic structuresreminiscent of multiwall carbon nanotubes (MWNT) seem to have beengenerated as a result of the high temperature reaction. These structuresare shown in FIG. 1-D.

[0135] The fluorination of MWNT has been reported previously (Hamwi, etal., 1997, Carbon, 35:723-728). This was done at two temperatures: 25°C. and 500° C. The room temperature reaction was done with a F₂, HF andIF₅ mixture and yielded an intercalated type compound. The reactioncarried out at 500° C. was done with F₂, and was determined to havedestroyed the tube structure to yield a graphite fluoride compound ofstoichiometry CF. In light of this, it is not too surprising thatdestruction of the SWNT was observed at 500° C., but somewhat surprisingthat MWNT-like structures are formed. The generation of these may be aconsequence of residual metal catalysts present in the sample.

[0136] Table 1. Reaction product stoichiometries determined by bothgravimetric and electron microprobe analysis. Reaction temp. ° C. 150250 325 400 500 600 gravimetric CF_(0.114) CF_(0.521) CF_(0.495)CF_(0.565) * microprobe CF_(0.097) CF_(0.458) CF_(0.554) CF_(0.647)CF_(0.815) CF_(0.990)

[0137] 1.2 Delfuorination of Single-Wall Carbon Nanotubes

[0138] Once fluorinated, SWNT were defluorinated with anhydroushydrazine (Aldrich, 98%). To the pieces of “bucky paper”, fluorinated at250° C., 325° C. and 400° C., was added 5 ml of hydrazine under an inertatmosphere at room temperature. The SWNT were allowed to sit in thehydrazine for one hour prior to filtering and washing with water.

[0139] As the Raman spectroscopy of SWNT has been well developed boththeoretically (Richter, et al., 1997, Phys, Rev. Lett., 79:2738-2741)and experimentally (Rao, et al., 1998, Science, 275:187-191), it wasused to examine the results of both the fluorination and subsequentdefluorination of the SWNT. FIG. 2 shows the Raman spectrum of the pure,unadulterated SWNT material. The smaller peak at 186 cm⁻¹ is due to acharacteristic breathing mode of the SWNT. Raman spectra of SWNTfluorinated for 5 hours at reaction temperatures of 250° C., 325° C. and400° C. are shown in FIG. 3. Trace A, corresponding to the reaction at250° C., shows only two broad peaks centered around 1340 cm⁻¹ and 1580cm⁻¹ and a broad band fluorescence. The Raman peaks correspond to sp³and sp² carbon stretching modes, respectively. At higher reaction temps,yielding high F to C ratios, these peaks disappear and the fluorescenceis attenuated. As C—F bonds are not very polarizable, it isunderstandable that they are not seen in the Raman spectra presentedhere.

[0140] Raman spectra of the defluorinated products of the SWNToriginally fluorinated at 250° C., 325° C. and 400° C. are shown in FIG.4. Traces A, B and C correspond to the material originally fluorinatedat 250° C., 325° C. and 400° C., respectively. As can be seen in tracesA and B, the characteristic breathing mode at 186 cm⁻¹ returns upondefluorination. This is not true in trace C, indicating that the tubesare largely destroyed at 400° C. Additionally, the peak at 1340 cm⁻¹grows relative to the characteristic SWNT peaks with increasingfluorination temperature. This can be attributed to one or both of thefollowing factors: one, tubes are being “unzipped” much more readily atthe higher temperatures and secondly, at higher reaction temperatures, agreater amount of decomposition of the type: CF₄, C₂F₄, C₂F₆, etc, isoccurring.

[0141] SEM images and two-point resistivity measurements were obtainedon a single piece of “bucky paper” after each of the following stages:purification, fluorination at 325° C. and defluorination in hydrazine atroom temperature for one hour. FIG. 5-A shows the purified startingmaterial. FIG. 5-B shows the same piece after having been fluorinated at325° C. for 5 hours. The image shows excessive charging due to itsinsulating nature, but the “rope-like” structure of tubes is stillevident. Finally, FIG. 5-C shows the same piece of “bucky paper” afterhaving been defluorinated in hydrazine. The two-point resistance of thepurified starting material is 15-16Ω measured 5 mm across the surface ofthe “bucky paper”. Identical measurements on the fluorinated anddefluorinated “bucky paper” yielded a resistance of >20 MΩ and 125-130Ωrespectively. It is interesting to note that the defluorinated materialrecovers most, but not all of its original conductivity.

Example 2

[0142] 2.1 Preparation of Fluorinated Single-Wall Carbon Nanotubes

[0143] SWNT were produced by the dual pulsed laser vaporization of Co/Nidoped graphite rods and purified as discussed previously (Rinzler, etal., 1998). The highly purified product consists of colloidallysuspended bundles or “ropes” of SWNT (Liu, et al., 1998). Filtering thisover a 0.2 micron PTFE filter membrane and rinsing with methanol yieldsa black film that can be peeled off to give a freestanding “buckypaper.” This paper was then oven baked for several hours at 150° C. toremove any residual solvent. The baked “bucky paper” was then loadedinto a temperature controlled monel flow reactor where it was purged at250° C. under a stream of He for ˜1 hour. A 10% F₂ in He mixture wasthen passed over the sample after first being passed over NaF to removeany HF present. This yielded material with stoichiometries ranging fromC₃F to C₂F (as determined by electron microprobe analysis) depending onreaction time (between 8 and 12 hours) and on the quantity beingfluorinated.

[0144] 2.2 Methylated Single-Wall Carbon Nanotubes

[0145] Once fluorinated, the nanotubes were then placed in a reactionflask under a N₂ purge. Methyl lithium (1.4 M in diethyl ether, Aldrich)was then added in significant molar excess via syringe through a rubberseptum in the reaction flask. The reaction mixture was then refluxed forthree hours and after which, the methyl lithium was neutralized with awater/ether mixture. The resulting material was then filtered, washedwith 3M HCI (to remove LiF and LiOH) followed by methanol and then ovendried at 130° C. Electron microprobe analysis revealed the fluorinecontent of this material to be 3.7 atomic percent (down from around30%). SEM and TEM analysis confirmed that the rope and tube structuressurvived both the fluorination and methylation steps.

[0146] The Raman spectroscopy of SWNT is now well known (Rao, et al.,1998). Raman spectroscopy of the methylated nanotube product wasobtained on a Spex Triplemate specrometer equipped with a CCD detectorand using a 514.5 nm Ar laser excitation source. The spectrum revealsthat significant alteration has taken place (FIG. 6). Pyrolysis of thismaterial in Ar at 700° C. regenerates the original SWNT as evidenced byits Raman spectrum. TGA of the pyrolysis process reveals a 25% mass lossupon heating to 700° C. EI mass spectroscopy of the pyrolysis productsreveals CH₃ groups to be the major species being evolved during thepyrolysis (FIG. 7) with the rest of the mass peaks being consistent withmethyl recombination pathways during pyrolysis.

[0147] The electrical properties of the SWNT change dramatically as theyare functionalized. The untreated SWNT are essentially metallic andtheir two point resistance (essentially a contact resistance, Bozhko, etal., 1998, Appl. Phys. A, 67:75-77) measured across 5 mm of the “buckypaper” surface is 10-15 Ω. When fluorinated, the tubes become insulatingand the two point resistance exceeds 20 M Ω. After methylation the tubespossess a two point resistance of ˜20 kΩ. Pyrolysis of the methylatedproduct brings the resistance down to ˜100 Ω. Incomplete return of theelectrical conductivity upon pyrolysis may be due to an increasedcontact resistance that results from disorder induced into the ropelattice following the sequence of reaction steps.

[0148] The methylated SWNT could be suspended quite readily bysonication in chloroform. Dispersal of this suspension on a Si waferfollowed by AFM analysis confirmed the nondestructive nature of thesonication process. Additionally, a large number of single tubes couldbe seen. This was not true of similarly exposed, untreated SWNT.

[0149] To get an infrared spectrum of the product, the dried methylatedmaterial was suspended in CDCl₃ and dispersed over KBr powder which wasthen dried and pressed into a pellet. By using deuterated chloroform weeliminated the possibility of seeing C—H stretching modes due to thepresence of residual solvent. IP analysis of the pellet revealed asignificant amount of C—H stretching in the ˜2950 cm⁻¹ region of thespectrum as shown in FIG. 8. Also present, however, is a significant C—Fstretching band indicating that not all of the fluorine had beendisplaced. This might be because the bulky methyl lithium cannotpenetrate the rope lattice to the extent that the fluorine could in theoriginal fluorination. Alternatively, the cage is likely to become lesselectronegative and, therefore, less susceptible to nucleophilic attackas successive fluorines are displaced (see Boltalina, et al., 1996, J.Chem. Soc., Perkin Trans., 2:2275-2278).

[0150] The methylated tubes were not suspendable in any of the nonpolarhydrocarbon solvents tried, although not all possibilities wereinvestigated. The fact that the suspendability of the methylated tubesin CHCl₃ is superior to that of the untreated tubes is interesting,however. Using a suitable solvent to suspend the methylated SWNT asindividual tubes capable of being manipulated individually, will havesignificant benefits. Alternatively, other nucleophiles, e.g. butyl, canbe substituted for the fluorine to render the SANT more suspendable in asuitable solvent, which is equally significant.

[0151] In summary, SWNT were methylated by first fluorinating them andthen reacting the fluorinated product with methyl lithium. Thismethylation of fluorinated SWNT precursors proceeds through a novelnucleophilic substitution pathway that is capable of generating a widerange of substituted SWNT products.

Example 3

[0152] 3.1 Preparation of Highly Purified SWNTs

[0153] Single wall carbon nanotubes were produced by the dual pulsedlaser vaporization of Co/Ni doped graphite rods and purified by methodsdiscussed previously (Rinzler, et al., Appl. Phys.A, 1998, 67:9-37.).The SWNTs produced in this way are primarily (10,10) nanotubes. Thepurified product is a metastable colloidal suspension of SWNT “ropes”(bundles of tubes ranging from a few to 200 SWNTs, see Thess, et al.,Science 1996, 273, 483-487) in a 0.2% aqueous solution of Triton™ X-100surfactant. This was then filtered over a PTTE filter membrane(Sartorius, with 0.2 μm pore dimensions) and rinsed with methanol.Filtering this and rinsing with methanol leads to a final product whichis a freestanding “mat” or “bucky paper” of SWNTs that is approximately10 μm thick. Purity of the SWNTs was monitored via scanning electronmicroscopy (JEOL 6320F SEM). FIG. 9 shows a sample of typical purity.This product was then resuspended by sonication in dimethyl formamide(DMF; Fisher, HPLC grade). Such treatment is believed to “cut” the tubesat their defect sites and also seems to unravel the ropes somewhat,leading to bundles containing fewer SWNTs. This product was thenfiltered, rinsed and heated in an oven at 150° C. for 2 hours prior tofluorination. Sonication in DMF may result in smaller SWNT ropes andultimately lead to a more efficient fluorination.

[0154] 3.2 Preparation of Fluorinated SWNTs

[0155] The purified nanotubes (5-10 mg in the form of bucky paper) wereplaced in a temperature controlled fluorination reactor constructed ofMonel™ and nickel. After sufficient purging in He (Trigas 99.995%) at250° C., fluorine (Air Products 98%, purified of HF by passing it overNaF pellets) was introduced. The fluorine flow was gradually increasedto a flow rate of 2 sccm diluted in a He flow of 20 sccm. Thefluorination was allowed to proceed for approximately 10 hours, at whichpoint the reactor was brought to room temperature, and the fluorine flowwas gradually lowered. After the fluorine flow was completely halted,the reactor was purged at room temperature for approximately 30 minutesbefore removing the fluorinated product. The fluorinated SWNTs consistedof approximately 70 atomic percent carbon and 30 atomic percent fluorineas determined by electron microprobe analysis (EMPA, Cameca SX-50). Thisfluorinated product was well characterized with Raman, IR, SEM, TEM,resistance measurements and x-ray photoelectron spectroscopy (PhysicalElectronics PHI 5700 XPS using soft monochromatic Al Kα (1486.7 eV)x-rays).

[0156] 3.3 Solvation in Alcohols

[0157] Attempts to solubilize fluorotubes with the “like dissolves like”approach of sonicating and heating them in perfluorinated solvents metwith little success. Attempts were also made to solvate them in hydrogenbonding solvents. Recent studies on the hydrogen bonding capabilities ofalkyl fluorides suggest that the fluorine in such species are poorhydrogen bond acceptors (Dunitz, et al., R, Eur. J. Chem., 1997,3(1):89-98; Howard, et al., Tetrahedron, 1996, 52(38):12613-12622). TheF⁻ion, however, is one of the best hydrogen bond acceptors available.The strength of the hydrogen bond formed between HF and F⁻ approximatesthat of a covalent bond (Harrell, et al., JA CS 1964, 86:4497). An XPSanalysis of our fluorinated SWNT product reveals an F 1s peak at abinding energy of 687 eV. Polytetrafluoroethylene has an F 1s bindingenergy of 691.5 eV. This suggests that the fluorine bonded to thefluorotubes is considerably more ionic than the fluorine present inalkyl fluorides (sce Watanabe, et al., Graphite Fluorides, Elsevier:Amsterdam, 1988; p.246). Thus, the increased ionic nature of the C—Fbond in the fluorotubes may make the fluorine on it better hydrogen bondacceptors.

[0158] Sonication of the fluorinated SWNT material in alcohols wascarried out by placing approximately 1 milligram of material into a vialcontaining approximately 10 mL of alcohol solvent and sonicating forapproximately 10 minutes. Sonication was performed by partiallyimmersing the capped vial in a Cole-Parmer ultrasonic cleaner(containing water) operating at 55 kHz. The solvated fluorotubes werethen dispersed on a clean mica surface by means of a 3000 rpm rotaryspinner (Headway Research, Inc.) and examined with atomic forcemicroscopy (Digital Instruments Multimode SPM). The solvated fluorotubeswere also analyzed with a Shimadzu model 1601PC UV-vis spectrometerusing quartz cuvetts.

[0159] Fluorotubes were solvated by sonicating in alcohol solventsincluding: methanol, ethanol, 2,2,2-trifluoroethanol, 2-propanol,2-butanol, n-pentanol, n-hexanol, cyclohexanol and n-heptanol.Sonicating the fluorotubes in alcohol solvents produced metastablesolutions. These solutions were stable for a couple of days to over oneweek, depending on the concentration and solvent used. While typicalsonication times were around 10 minutes, the heavier solvents (pentanoland up) required slightly longer sonication times in order to fullysuspend the tubes. Of the solvents used, 2-propanol and 2-butanol seemedto solvate the fluorotubes the best with the solutions being stable formore than a week. The solubility limit of the solvated “fluorotubes” in2-propanol is at least 0.1 mg/mL. This solution was stable for slightlyless than a week with some particulate matter precipitating out after afew days. This suggests that pushing the solubility limit somewhatdecreases the solution's stability or that a super saturated solutioncan exist for a shorter period of time. All of the other solutions werestable for at least a couple of days before the onset of precipitation.A likely scenario for such solvation would be hydrogen bonding betweenthe alcohol's hydroxyl hydrogen and the nanotubebound fluorine (scheme1). No evidence of alkoxy substitution (or evolution of HF) wasobserved.

[0160] Efforts were also made to solvate the fluorotubes in other stronghydrogen bonding solvents like water, diethyl amine, acetic acid andchloroform. While water will not “wet” the fluorotube by itself, it willwith the addition of a small amount of acetone. Still, even longsonication times in this water/acetone mixture failed to solvate thefluorotubes. Likewise, neither diethylamine nor acetic acid wouldsolvate the fluorotubes. Chloroform solvated the tubes, but the solutionwas far less stable than those in alcohol solvents, with the fluorotubesfalling out of solution in less than an hour.

[0161] The solvated fluorotubes were filtered over a 0:2 micron PTFEfilter. Once dry, the fluorotubes could be peeled off the paper to forma freestanding film. This film was then examined by Raman spectroscopy(Jobin Yvon-Spex model HR 460 monochrometer coupled with an ISA SpectrumONE series CCD detector and using 514.5 nm excitation from a Liconix Arlaser) and by EMPA to determine whether or not any reaction had takenplace on the basis of the composition of the product. Fluorotubes fromall of the solutions (except those in cyclohexanol, n-hexanol andn-heptanol) were examined with atomic force microscopy. FIG. 10 shows anAFM scan of fluorotubes that had been dissolved in 2-butanol and thendispersed on a clean mica surface. This result is fairly typical of allthe fluorotube/alcohol solutions that were examined with AFM. Almost allthe tubes are believed to be solvated, as few “ropes” (bundles of tubes)are present.

[0162] Some of these solutions were examined with ¹⁹F-NMR, but thisproved to be rather uninformative. It yielded abroad peak centered ataround −175 ppm. While this is indicative of fluorine being present, thebroadening is due to either a wide variety of F environments (as seen inthe inhomogeneous fluorination of C₆₀, Kniaz, et al., J Am. Chem. Soc.,1993,115:6060-6064) or of insufficient “tumbling” while in solution. Noinformation regarding the possible hydrogen bonding environments couldbe obtained with this method.

[0163] Filtering a solution of fluorotubes in isopropyl alcohol over aPTFE filter and examining the tubes with EMPA revealed no presence ofoxygen and only slightly lower fluorine levels (C/F atomic percentratio=72/28 compared with 70/30 for the starting material). This wouldsuggest that the solvation process is not the result of a chemicalreaction, but is instead the result of hydrogen bonding between thealcohol and the fluorines on the nanotube surface. Analysis offluorotubes sonicated for much longer times (2 hours) showed reducedlevels of fluorine (C/F atomic percent ratio=76/24), yet they remainedsolvated. Apparently, ultrasonication can lead to removal of some of thefluorine if allowed to progress long enough. The fluorotubes weresonicated continuously in isopropanol and monitored with UV-visabsorption spectroscopy for sonication time t=10 minutes and every 30minutes after that. After sonication for 40 minutes the solutionexhibited an absorption band at 204 nm. This band continued to grow andto red shift to lower energy as the sonication proceeded and fluorinewas presumably being eliminated. After sonicating for 130 minutes thepeak had increased in intensity and shifted to 237 nm (FIG. 11).

[0164] 3.4 Reactions in Solution

[0165] The present inventors shown that hydrazine acts as a effectivedefluorinating agent. Anhydrous hydrazine (Aldrich, 98%) was added tothe solvated fluorotubes. The reaction mixture was continually stirredwith a glass stir bar for a period of about an hour. The reactionmixture was filtered, rinsed with methanol and allowed to dry. Thisproduct was then examined with EMPA and Raman spectroscopy. It was alsosuspended in dimethyl formamide, dispersed on a mica surface andexamined with AFM. The instruments and procedures were as above.

[0166] Adding anhydrous hydrazine to a solution of fluorotubes inisopropanol caused them to immediately precipitate out of solution.Filtering the solution after letting it sit for an hour yielded aproduct of very low fluorine content, as determined by EMPA (C/F atomicpercent ratio=93/7). Unreacted SWNTs are known to suspend fairly well inDMF. Suspending this product in DMF and dispersing it on a mica surfacefollowed by AFM analysis yielded tubes very reminiscent of the startingmaterial (FIGS. 12, a & b).

[0167] Raman spectroscopy of SWNTs has been well established (Richter,E., et al., Phys. Rev. Lett., 1997, 79(14):2738-2741; Rao, et al.,Science, 1997, 275:187-191; Fang, et al., J. Mat. Res., 1998,13:2405-2411), and it was used as a probe to follow the startingmaterial through the fluorination, sonication and defluorination. Ramanspectroscopy on the hydrazine-defluorinated product yields a spectrumsimilar to the starting material and very different from the fluorinatedSWNTs (FIGS. 13; ab & c).

[0168] Fluorotubes were also sonicated in a 0.5 M sodium methoxide inmethanol solution (Aldrich, A. C. S. reagent) for approximately 10minutes. The tubes broke up and appeared to be suspended but quicklyfell out of solution upon standing. This too was filtered, rinsed andexamined with EMPA and EI mass spectroscopy (Finnigan MAT 95)

[0169] Sonication of the fluorotubes in a sodium methoxide in methanolsolution for two hours resulted in the tubes precipitating out ofsolution. After the filtered product was rinsed with water (to removeNaF) and methanol, then dried in an oven at 140° C. for half an hour, itwas analyzed with EMPA which revealed the C/F/O relative atomic percentsto be 79/17/4. This varies considerably from the starting material whichhad C/F/O relative atomic percents of 66/33.7/0.3 and suggests a productsoichiometry of C_(4.4)F(OCH₃)_(0.25). Pyrolysis of this product with ahigh temperature probe inside a mass spectrometer, followed by electronionization, yielded significant quantities of methoxy ions (m/z=31)coming off primarily at 650-700° C. as determined by the residual ioncurrent trace. The high temperature for evolution indicates that themethoxy groups seen were originally strongly bonded to the nanotube. Ifthe oxygen ratios seen by EMPA are reflective of the number of methoxygroups present on the nanotube, it may be concluded that the majority ofthese would have to be bonded to the nanotube side wall, based on thefact that the number of nanotube end carbons is extremely small relativeto the number of side wall carbons.

[0170] Nucleophilic attack on the fluorinated nanotube by a methoxyanion is a plausible scenario as nucleophilic attack of this type hasbeen well documented in the case of fluorinated fullerenes (Mickelson,et al., J Fluorine Chem 1998, 92(l):59-62; Taylor, et al., J. Chem.Soc., Chem. Commun. 1992,665-667). The C—F bonds on fluorinatedfullerenes (and carbon nanotubes) are weakened relative to the C—F bondsin alkyl fluorides due to an “eclipsing strain effect” (Taylor, R,.Russian Chemical Bulletin, Engl. Ed. 1998, 47(5):823-832). Anucleophilic attack of this type is likely to occur via attack on anelectropositive carbon beta to a carbon with fluorine attached to it asshown in scheme 2. This is rationalized by the fact that an S_(N)1 typesubstitution is energetically unfavorable end backside attack, as in anS_(N)2 type mechanism, is impossible (Taylor, R The Chemistry of theFullerenes (Edited by R. Taylor), World Scientific Publishing, London,1995; pp. 208-209).

[0171] Molecular Arrays of Single-Wall Carbon Nanotubes

[0172] An application of particular interest for a homogeneouspopulation of SWNT molecules is production of a substantiallytwo-dimensional array made up of single-walled nanotubes aggregating(e.g., by van der Waals forces) in substantially parallel orientation toform a monolayer extending in directions substantially perpendicular tothe orientation of the individual nanotubes. Formation of such arrays issubstantially enabled by derivatization of both the ends and side wallsof nanotubes as is indicated below. Such monolayer arrays can be formedby conventional techniques employing “self-assembled monolayers” (SAM)or Langmiur-Blodgett films, see Hirch, pp. 75-76. Such a molecular arrayis illustrated schematically in FIG. 14. In this figure, derivatizednanotubes 1 are bound via interaction of the linking or complexingmoiety attached to the nanotube to a substrate 2 having a reactivecoating 3 (e.g., gold). Sidewall derivatization in this application canfacilitate assembly of the array by enabling the tubes to moveeffectively together as the array assembles.

[0173] Typically, SAMs are created on a substrate which can be a metal(such as gold, mercury or ITO (indium-tin-oxide)). The molecules ofinterest, here the SWNT molecules, are linked (usually covalently) tothe substrate through a linker moiety such as —S—, —S—(CH₂)_(n)—NH—,—SiO₃(CH₂)₃NH— or the like. The linker moiety may be bound first to thesubstrate layer or first to the SWNT molecule (at an open or closed end)to provide for reactive self-assembly. Langmiur-Blodgett films areformed at the interface between two phases, e.g., a hydrocarbon (e.g.,benzene or toluene) and water. Orientation in the film is achieved byemploying molecules or linkers that have hydrophilic and lipophilicmoieties at opposite ends. The configuration of the SWNT molecular arraymay be homogenous or heterogeneous depending on the use to which it willbe put. Using SWNT molecules of the same type and structure provides ahomogeneous array of the type shown in FIG. 14. By using different SWNTmolecules, either a random or ordered heterogeneous structure can beproduced. An example of an ordered heterogeneous array is shown in FIG.15 where tubes 4 are (n,n), i.e., metallic in structure and tubes 5 are(m,n), i.e., insulating. This configuration can be achieved by employingsuccessive reactions after removal of previously masked areas of thereactive substrate.

[0174] Arrays containing from 10³ up to 10¹⁰ and more SWNT molecules insubstantially parallel relationships can be used per se as a nanoporousconductive molecular membrane, e.g., for use in fuel cells and inbatteries such as the lithium ion battery. This membrane can also beused (with or without attachment of a photoactive molecule such ascis-(bisthiacyanato bis (4,4′-dicarboxy-2-2′-bipyridine Ru (II)) toproduce a highly efficient photo cell of the type shown in U.S. Pat. No.5,084,365.

[0175] One preferred use of the SWNT molecular arrays of the presentinvention is to provide a “seed” or template for growth of macroscopiccarbon fiber of single-wall carbon nanotubes as described below. The useof a macroscopic cross section in this template is particularly usefulfor keeping the live (open) end of the nanotubes exposed to feedstockduring growth of the fiber. The template array of this invention can beused as formed on the original substrate, cleaved from its originalsubstrate and used with no substrate (the van der Waals forces will holdit together) or transferred to a second substrate more suitable for theconditions of fiber growth.

[0176] Where the SWNT molecular array is to be used as a seed ortemplate for growing macroscopic carbon fiber as described below, thearray need not be formed as a substantially two-dimensional array. The“seed” array can, for instance, be the end of a fiber of parallelnanotubes in van der Waals contact that has been cut, or a short segmentof such a fiber that has been cut from the fiber. For such substratesthe surface comprising the ends of must be prepared to be clean and flatby polishing and or electrochemical etching to achieve a clean, highlyplanar surface of exposed nanotube ends. Any form of array that presentsat its upper surface a two-dimensional array can be employed. In thepreferred embodiment, the template molecular array is a manipulatablelength of macroscopic carbon fiber as produced below.

[0177] Large arrays (i.e., >10⁶ tubes) also can be assembled usingnanoprobes by combining smaller arrays or by folding linear collectionsof tubes and/or ropes over (i.e., one folding of a collection of n tubesresults in a bundle with 2n tubes).

[0178] Growth of Nanotubes from “Seeds”

[0179] The present invention provides methods for growing continuouscarbon fiber from SWNT molecular arrays to any desired length. Thecarbon fiber which comprises an aggregation of substantially parallelcarbon nanotubes may be produced according to this invention by growth(elongation) of a suitable seed molecular array. As used herein, theterm “macroscopic carbon fiber” refers to fibers having a diameter largeenough to be physically manipulated, typically greater than about 1micron and preferably greater than about 10 microns.

[0180] It is well known that SWNT formation occurs at temperaturesbetween 500 and 2000° C. in which a catalytic particle comprising GroupVI B or VIII B Btransition metals (individually or as a mixture) residesat the end of a “growing” SWNT. The catalytic particle interacts with acarbon-bearing feedstock to promote chemical processes by which carbonin the feedstock is converted into carbon organized in the structureknown as a SWNT. Once a SWNT of a specific geometry (chirality anddiameter) begins to grow, the tube geometry remains fixed. The catalytictube-growth process is most effectively promoted by catalyst particlesof an appropriate size range and chemical composition. Examples in theart indicate that the most effective catalyst particles have diametersapproximately equal to those of the growing nanotubes, and that theycomprise a single metal or a mixture of metals. An objective of thisinvention is to provide processes by which a suitable catalyst particlemay be formed at the end of an existing SWNT, enabling growth of thattube to be initiated upon introduction of the tube/catalyst-particleassembly to an appropriate environment.

[0181] To achieve the objective, the invention provides methods forassembling catalyst particles on the ends of individual fullerenesingle-wall nanotubes (SWNT) in a way that supports further growth ofthe SWNT. Deliberate initiation of SWNT growth from such “seed” tubes isuseful in that:

[0182] 1) it can act to produce nanotubes that have the same geometry asthe “seed” tubes. [It is well known that fullerene single wall nanotubes(SWNT) may be formed with different geometries (different diameters andarrangements of carbon atoms with respect to the tube axis), and thatthe physical properties (e.g., electrical conductivity) of these tubesgenerally depend on these geometries]. Control of the tube geometrypermits growth of SWNT for applications that require specific materialproperties.

[0183] 2) It can serve as an enabling process in bulk production ofnanotubes;

[0184] 3) It can enable growth of ordered structures of SWNT that havebeen assembled by other means (e.g., suitable arrays can be formed byconventional techniques employing “self-assembled monolayers” (SAM) orLangmiur-Blodgett films, see Hirch, pp. 75-76.

[0185] 4) It can be used to grow structural shapes of SWNT materialcomprising parallel nanotubes all in van der Waals contact. Thesematerials can have the forms of sheets, I-beams, channels, etc. byappropriately configuring the seed in the shape of the cross section ofthe desired structural object.

[0186] To achieve the objectives and provide the benefits of growth from“seeds,” the present invention provides:

[0187] 1) A measured amount of a transition-metal-containing species ischemically attached (by covalent bonding, chemisorption, physisorptionor combination thereof) to the sidewall of an individual SWNT segment orto the sidewalls of a group of SWNT segments. A preferred embodiment isone in which the metal is contained as a compound that is stable toexposure to moisture and air. The amount of metal attached to the SWNTsegment is determined by the degree of derivatization, which is definedherein as the number of derivative sites per nanometer of tube length.In this invention, the preferred degree of derivatization isapproximately 1 per nanometer, and the preferred method ofderivatization is covalent bonding of a species that contains a metalatom. Alternatively, the transition metal may be deposited directly onthe surface from metal vapor introduced onto the open tube ends of the“seed”.

[0188] 5) Chemical or physical processing of the metal ormetal-containing species in a way that allows metal atoms to aggregateat or near the end of the tube segment so that the aggregate is asuitable catalyst for enabling growth of the tube when the tube/catalystassembly is introduced to an appropriate environment.

[0189] 6) Growth of nanotubes of specific geometries (chirality anddiameter) by choosing the diameter and chirality of the “seed” tube.

[0190] 7) Growth of organized structures of SWNT (e.g., arrays of tubeswith specific relative spacing and orientation of individual tubes,membranes of tubes comprising many parallel tubes closely packedtogether, and rods or fibers of tubes with parallel axes) in which aninitial structure has been assembled by other means, which include theoperation of molecule agencies attached to the sidewalls of the SWNTsforming the structure, and the novel compositions of matter so produced.

[0191] 8) Growth of organized structures of SWNT (as 4 above) in whichthe SWNT all have the same geometry (chirality and diameter) and thecomposition of matter so produced.

[0192] 9) Growth of organized structures of SWNT (as 4 above) in whichthe SWNT all have a range of geometries chosen to perform a specificfunction (e.g., a core of tubes of conducting geometry surrounded bytubes of large-gap semiconducting geometry to effect a small “insulatedwire”) and the structures so produced.

[0193] 10) Production of “monoclonal” batches of tubes that all haveprecisely the same geometry because they all are grown from segments ofa single tube which has been cut by known techniques and thecompositions of matter so produced.

[0194] The present invention is further exemplified by the following:

[0195] a) A process in which one cuts segments of SWNT of 0.1 to 1micron length by, for instance, sonicating the SWNT material indimethylformamide, selects tube segments of a specific range of lengthand covalently bonds a chelating agent such as ethylene to the tubewall. These binding sites are sufficiently spaced from one another thatthe number of chelating agent molecules is roughly equivalent to thenumber of metal atoms needed to form an active catalyst cluster at theend of the tube segment. Covalent bonding of various species isdescribed herein, via replacement reactions upon a small fraction of thederivatized sites on fluorinated tubes. A chelating agent is reactedwith a fluorinated SWNT so that the chelating agent replaces fluorine onthe nanotube, followed by washing the derivatized nanotube with a weaksolution of metal ions in water (e.g., Fe³⁺). The interaction of the Feand water with the chelating agent will form a complex on the tubesurface that is stable under exposure to air and water. The tubematerial can be heated in a reducing atmosphere (such as H₂). Thisheating will cause the chelating agent to react by converting to gaseousproducts, leaving Fe adsorbed on the tube wall, and at appropriatetemperatures the Fe will migrate along the tube walls. The tube endpresents an irregularity of the surface upon which the Fe is migrating,and the Fe will preferentially collect there as an aggregate suitablefor functioning as a catalyst particle for tube growth.

[0196] b) Approaches similar to a) above, but including more complex,multidentate ligands such as ethydiamine tetra-acetic acid (EDTA) orbipyridine tethered to the side of the SWNT by a covalent linkage orsimpler species such as a carboxylate or OH group.

[0197] c) Another means for assembly of a catalytic particle at the endof an SWNT segment involves reaction processes in which chelatingagents, other ligands, or metal containing species themselves, arechemically attached to the tube ends (both open and closed). Asdescribed above, the tube ends are more active sites and support abroader range of chemical processes than the tube sidewalls. Bothion-exchange and covalent attachment of metal-bearing proteins (e.g.metallothionein) or metal-bearing complexes are possible examples. Onecan, for example, exchange the metal atoms for the carboxylic acidgroups known to exist at the ends of tubes, directly attached metalbearing proteins or other metal-containing species with the tube ends.If necessary further processes can enable deposition of additional metalat the ends of the tube segments. The amount of metal is simplydetermined by the usual methods of control of the reagentconcentrations, temperatures, and reaction times. Here, again,aggregates of metal atoms of the appropriate size are formed at the endof selected SWNT segments, and can serve as catalysts for tube growthunder the appropriate conditions.

[0198] d) Formation of arrays of SWNT wherein the array formation isenabled and controlled by species attached to the tube sidewalls. Thisspecies that enables array formation may be attached to the tube bycovalent bonding, chemisorption, adsorption, or a combination thereof.This aspect of this invention:

[0199] i) enables and controls organization of SWNT segments intoorganized structures and

[0200] ii) admits metal-containing species or metal atoms or ions to thetube sidewalls in a way that under appropriate chemical processing themetal particles may migrate to the tube ends and form catalysts forfurther SWNT growth.

[0201] The first step in the growth process is to open the growth end ofthe SWNTs in the molecular array. This can be accomplished as describedabove with an oxidative and/or electrochemical treatment. Next, atransition metal catalyst is added to the open-ended seed array. Thetransition metal catalyst can be any transition metal that will causeconversion of the carbon-containing feedstock described below intohighly mobile carbon radicals that can rearrange at the growing edge tothe favored hexagon structure. Suitable materials include transitionmetals, and particularly the Group VI B or VIII B transition metals,i.e., chromium (Cr), molybdenum (Mo), tungsten (W), iron (Fe), cobalt(Co), nickel (N1), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium(Os), iridium (Ir) and platinum (Pt). Metals from the lanthanide andactinide series may also be used. Preferred are Fe, Ni, Co and mixturesthereof. Most preferred is a 50/50 mixture (by weight) of Ni and Co.

[0202] The catalyst should be present on the open SWNT ends as a metalcluster containing from about 10 metal atoms up to about 200 metal atoms(depending on the SWNT molecule diameter). Typically, the reactionproceeds most efficiently if the catalyst metal cluster sits on top ofthe open tube and does not bridge over adjacent tubes. Preferred aremetal clusters having a cross-section equal to from about 0.5 to about1.0 times the tube diameter (e.g., about 0.7 to 1.5 nm).

[0203] In the preferred process, the catalyst is formed, in situ, on theopen tube ends of the molecular array by a vacuum deposition process.Any suitable equipment, such as that used in Molecular Beam Epitaxy(MBE) deposition, can be employed. One such device is a Küdsen EffusionSource Evaporator. It is also possible to effect sufficient depositionof metal by simply heating a wire in the vicinity of the tube ends(e.g., a Ni/CO wire or separate Ni and CO wires) to a temperature belowthe melting point at which enough atoms evaporate from one wire surface(e.g., from about 900 to about 1300° C.). The deposition is preferablycarried out in a vacuum with prior outgassing. Vacuums of about 10⁻⁶ to10 ⁻⁸ Torr are suitable. The evaporation temperature should be highenough to evaporate the metal catalyst. Typically, temperatures in therange of 1500 to 2000° C. are suitable for the Ni/Co catalyst of thepreferred embodiment. In the evaporation process, the metal is typicallydeposited as monolayers of metal atoms. From about 1-10 monolayers willgenerally give the required amount of catalyst. The deposition oftransition metal clusters on the open tube tops can also be accomplishedby laser vaporization of metal targets in a catalyst deposition zone.

[0204] The actual catalyst metal cluster formation at the open tube endsis carried out by heating the tube ends to a temperature high enough toprovide sufficient species mobility to permit the metal atoms to findthe open ends and assemble into clusters, but not so high as to effectclosure of the tube ends. Typically, temperatures of up to about 500° C.are suitable. Temperatures in the range of about 400-500° C. arepreferred for the Ni/Co catalysts system of one preferred embodiment.

[0205] In a preferred embodiment, the catalyst metal cluster isdeposited on the open nanotube end by a docking process that insuresoptimum location for the subsequent growth reaction. In this process,the metal atoms are supplied as described above, but the conditions aremodified to provide reductive conditions, e.g., at 800° C., 10 millitorrof H₂ for 1 to 10 minutes. There conditions cause the metal atomclusters to migrate through the system in search of a reactive site.During the reductive heating the catalyst material will ultimately findand settle on the open tube ends and begin to etch back the tube. Thereduction period should be long enough for the catalyst particles tofind and begin to etch back the nanotubes, but not so long as tosubstantially etch away the tubes. By changing to the above-describedgrowth conditions, the etch-back process is reversed. At this point, thecatalyst particles are optimally located with respect to the tube endssince they already were catalytically active at those sites (albeit inthe reverse process).

[0206] The catalyst can also be supplied in the form of catalystprecursors which convert to active form under growth conditions such asoxides, other salts or ligand stabilized metal complexes. As an example,transition metal complexes with alkylamines (primary, secondary ortertiary) can be employed. Similar alkylamine complexes of transitionmetal oxides also can be employed. The catalyst can also be added to thefree ends by causing migration of metal atoms derived from side wallpendant groups added as described above.

[0207] In the next step of the process of the present invention, theSWNT molecular array with catalyst deposited on the open tube ends issubjected to tube growth (extension) conditions. This may be in the sameapparatus in which the catalyst is deposited or a different apparatus.The apparatus for carrying out this process will require, at a minimum,a source of carbon-containing feedstock and a means for maintaining thegrowing end of the continuous fiber at a growth and annealingtemperature where carbon from the vapor can be added to the growing endsof the individual nanotubes under the direction of the transition metalcatalyst. Typically, the apparatus will also have means for continuouslycollecting the carbon fiber. The process will be described forillustration purposes with reference to the apparatus shown in FIGS. 16and 17.

[0208] The carbon supply necessary to grow the SWNT molecular array intoa continuous fiber is supplied to the reactor 10, in gaseous formthrough inlet 11. The gas stream should be directed towards the frontsurface of the growing array 12. The gaseous carbon-containing feedstockcan be any hydrocarbon or mixture of hydrocarbons including alkyls,acyls, aryls, aralkyls and the like, as defined above. Preferred arehydrocarbons having from about 1 to 7 carbon atoms. Particularlypreferred are methane, ethane, ethylene, actylene, acetone, propane,propylene and the like. Most preferred is ethylene. Carbon monoxide mayalso be used and in some reactions is preferred. Use of CO feedstockwith transition metal catalysts is believed to follow a differentreaction mechanism than that proposed for most other feedstock gasses.See Dai, et al., 1996.

[0209] The feedstock concentration is preferably as chosen to maximizethe rate of reaction, with higher concentrations of hydrocarbon givingfaster growth rates. In general, the partial pressure of the feedstockmaterial (e.g., ethylene) can be in the 0.001 to 1000.0 Torr range, withvalues in the range of about 1.0 to 10 Torr being preferred. The growthrate is also a function of the temperature of the growing array tip asdescribed below, and as a result growth temperatures and feed stockconcentration can be balanced to provide the desired growth rates. Apreferred feedstock in many instances is CO, in which case the optimalpressures are in the range of 10 to 100 atmospheres.

[0210] It is not necessary or preferred to preheat the carbon feedstockgas, since unwanted pyrolysis at the reactor walls can be minimizedthereby. The only heat supplied for the growth reaction should befocused at the growing tip of the fiber 12. The rest of the fiber andthe reaction apparatus can be kept at room temperature. Heat can besupplied in a localized fashion by any suitable means. For small fibers(<1 mm in diameter), a laser 13 focused at the growing end is preferred(e.g., a C—W laser such as an argon ion laser beam at 514 nm). Forlarger fibers, heat can be supplied by microwave energy or R—F energy,again localized at the growing fiber tip. Any other form of concentratedelectromagnetic energy that can be focused on the growing tip can beemployed (e.g., solar energy). Care should be taken, however, to avoidelectromagnetic radiation that will be absorbed to any appreciableextent by the feedstock gas.

[0211] The SWNT molecular array tip should be heated to a temperaturesufficient to cause growth and efficient annealing of defects in thegrowing fiber, thus forming a growth and annealing zone at the tip. Ingeneral, the upper limit of this temperature is governed by the need toavoid pyrolysis of the feedstock and fouling of the reactor orevaporation of the deposited metal catalyst. For most feedstocks andcatalysts, this is below about 1300° C. The lower end of the acceptabletemperature range is typically about 500° C., depending on the feedstockand catalyst efficiency. Preferred are temperatures in the range ofabout 500° C. to about 1200° C. More preferred are temperatures in therange of from about 700° C. to about 1200° C. Temperatures in the rangeof about 900° C. to about 1100° C. are the most preferred, since atthese temperatures the best annealing of defects occurs. The temperatureat the growing end of the cable is preferably monitored by, andcontrolled in response to, an optical pyrometer 14, which measures theincandescence produced. While not preferred due to potential foulingproblems, it is possible under some circumstances to employ an inertsweep gas such as argon or helium.

[0212] In general, pressure in the growth chamber can be in the range of1 millitorr to about 1 atmosphere. The total pressure should be kept at1 to 2 times the partial pressure of the carbon feedstock. A vacuum pump15 may be provided as shown. It may be desirable to recycle thefeedstock mixture to the growth chamber. As the fiber grows it can bewithdrawn from the growth chamber 16 by a suitable transport mechanismsuch as drive roll 17 and idler roll 18. The growth chamber 16 is indirect communication with a vacuum feed lock zone 19.

[0213] The pressure in the growth chamber can be brought to atmospheric,if necessary, in the vacuum feed lock by using a series of chambers 20.Each of these chambers is separated by a loose TEFLON O-ring seal 21surrounding the moving fiber. Pumps 22 effect the differential pressureequalization. A take-up roll 23 continuously collects the roomtemperature carbon fiber cable. Product output of this process can be inthe range of 10⁻³ to 10₁ feet per minute or more. By this process, it ispossible to produce tons per day of continuous carbon fiber made up ofSWNT molecules.

[0214] Growth of the fiber can be terminated at any stage (either tofacilitate manufacture of a fiber of a particular length or when toomany defects occur). To restart growth, the end may be cleaned (i.e.,reopened) by oxidative etching (chemically or electrochemically). Thecatalyst particles can then be reformed on the open tube ends, andgrowth continued.

[0215] The molecular array (template) may be removed from the fiberbefore or after growth by macroscopic physical separation means, forexample by cutting the fiber with scissors to the desired length. Anysection from the fiber may be used as the template to initiateproduction of similar fibers.

[0216] The continuous carbon fiber of the present invention can also begrown from more than one separately prepared molecular array ortemplate. The multiple arrays can be the same or different with respectto the SWNT type or geometric arrangement in the array. Large cable-likestructures with enhanced tensile properties can be grown from a numberof smaller separate arrays as shown in FIG. 18. In addition to themasking and coating techniques described above, it is possible toprepare a composite structure, for example, by surrounding a centralcore array of metallic SWNTs with a series of smaller circularnon-metallic SWNT arrays arranged in a ring around the core array asshown in FIG. 19.

[0217] Not all the structures contemplated by this invention need beround or even symmetrical in two-dimensional cross section. It is evenpossible to align multiple molecular array seed templates in a manner asto induce nonparallel growth of SWNTs in some portions of the compositefiber, thus producing a twisted, helical rope, for example. It is alsopossible to catalytically grow macroscopic carbon fiber in the presenceof an electric field to aid in alignment of the SWNTs in the fibers, asdescribed above in connection with the formation of template arrays.

[0218] Random Growth of Carbon Fibers From SWNTs

[0219] While the continuous growth of ordered bundles of SWNTs describedabove is desirable for many applications, it is also possible to produceuseful compositions comprising a randomly oriented mass of SWNTs, whichcan include individual tubes, ropes and/or cables. The random growthprocess has the ability to produce large quantities, i e., tons per day,of SWNT material.

[0220] In general the random growth method comprises providing aplurality of SWNT seed molecules that are supplied with a suitabletransition metal catalyst as described above, including the use of sidewall derivatization to supply the catalyst moiety and subjecting theseed molecules to SWNT growth conditions that result in elongation ofthe seed molecule by several orders of magnitude, e.g., 10² to 10¹⁰ ormore times its original length.

[0221] The seed SWNT molecules can be produced as described above,preferably in relatively short lengths, e.g., by cutting a continuousfiber or purified bucky paper. In a preferred embodiment, the seedmolecules can be obtained after one initial run from the SWNT feltproduced by this random growth process (e.g., by cutting). The lengthsdo not need to be uniform and generally can range from about 5 nm to 10μm in length.

[0222] These SWNT seed molecules may be formed on macroscale ornanoscale supports that do not participate in the growth reaction. Inanother embodiment, SWNTs or SWNT structures can be employed as thesupport material/seed. For example, the self assembling techniquesdescribed below can be used to form a three-dimensional SWNTnanostructure. Nanoscale powders produced by these techniques have theadvantage that the support material can participate in the random growthprocess.

[0223] The supported or unsupported SWNT seed materials can be combinedwith a suitable growth catalyst as described above, by opening SWNTmolecule ends and depositing a metal atom cluster. Alternatively, thegrowth catalyst can be provided to the open end or ends of the seedmolecules by evaporating a suspension of the seeds in a suitable liquidcontaining a soluble or suspended catalyst precursor. For example, whenthe liquid is water, soluble metal salts such as Fe (NO₃)₃, Ni (NO₃)₂ orCO (NO₃)₂ and the like may be employed as catalyst precursors. In orderto insure that the catalyst material is properly positioned on the openend(s) of the SWNT seed molecules, it may be necessary in somecircumstances to derivatize the SWNT ends with a moiety that binds thecatalyst nanoparticle or more preferably a ligand-stabilized catalystnanoparticle.

[0224] In the first step of the random growth process the suspension ofseed particles containing attached catalysts or associated withdissolved catalyst precursors is injected into an evaporation zone wherethe mixture contacts a sweep gas flow and is heated to a temperature inthe range of 250-500° C. to flash evaporate the liquid and provide anentrained reactive nanoparticle (i.e., seed/catalyst). Optionally thisentrained particle stream is subjected to a reduction step to furtheractivate the catalyst (e.g., heating from 300-500° C. in H₂). Acarbonaceous feedstock gas, of the type employed in the continuousgrowth method described above, is then introduced into the sweepgas/active nanoparticle stream and the mixture is carried by the sweepgas into and through a growth zone.

[0225] The reaction conditions for the growth zone are as describedabove, i.e., 500-1000° C. and a total pressure of about one atmosphere.The partial pressure of the feedstock gas (e.g., ethylene, CO) can be inthe range of about 1 to 100 Torr for ethylene or 1 to 100 atmospheresfor CO. The reaction with pure carbon or hydrocarbon feedstocks ispreferably carried out in a tubular reactor through which a sweep gas(e.g., argon) flows.

[0226] The growth zone may be maintained at the appropriate growthtemperature by 1) preheating the feedstock gas, 2) preheating the sweepgas, 3) externally heating the growth zone, 4) applying localizedheating in the growth zone, e.g., by laser or induction coil, or anycombination of the foregoing.

[0227] Downstream recovery of the product produced by this process canbe effected by known means such as filtration, centrifugation and thelike. Purification may be accomplished as described above. Felts made bythis random growth process can be used to make composites, e.g., withpolymers, epoxies, metals, carbon (i.e., carbon/carbon materials) andhigh −T_(c) superconductors for flux pinning.

[0228] Endohedrally-Doped Fullerene Carbon Nanocages

[0229] The present invention is for the fluorination of fullerene carbonnanocages as an efficient way to (a) facilitate synthesis of endohedralcomplexes by a significant reduction or elimination of the barriers forthe entry of guest-ions, -atoms or molecules, and (b) to preserve thechemical stability of final product. The fluorination of the fullerenecarbon nanocage exterior makes it easier for low-energy ions orthermally-excited atoms or molecules to “punch” their way through thenanocage wall by reducing the barrier for insertion as shown in FIG. 20.

[0230] The physical cause of these effects is the destruction of (or atleast a reduction in) the chemically-active π-electron system followedby the formation of new C—F covalent bonds (See FIG. 21). Quantumchemical and molecular dynamics simulations show that the penetrationbarrier can be reduced several times (e.g. for H⁺ 2-6 times, to almost1.5 eV), depending upon the precise point of entry (cage regionspossessing lower electron density will have lower barriers of entry). Asshown in FIG. 20 for C₆₀, for 25% of its surface, the penetrationbarrier can be reduced 3 times for H⁺. This permits the use of lowenergy ion beams or high pressure for insertion of radioactive isotopes(e.g. T⁺, T₂, ³He or for a series of cobalt isotopes of small ionicradius) into the cages (While by no means intended to be an exhaustiveset, see Table 2 below for a comparison of some radioactive specieswhich might be inserted into a fullerene carbon nanocage using themethods described herein.). At the same time, the analogous barriers forthe exit outside the cage remain high. This ensures that the activecomponent, and the radioactive decay products, are retained within thecage. TABLE 2 Data from CRC Handbook, CRC Press, Boca Raton, FL.Disintegration Isotope Half-life Decay Mode Energy Ionic Radius T⁺ (³H⁺)12.26 years β⁻ 0.0186 MeV 0.00 Å ⁶⁰Co²⁺  5.26 years γ  2.819 MeV 0.56 Å⁹⁰Sr²⁺  28.1 years β⁻  0.546 MeV 1.18 Å

[0231] High-pressure endohedral doping of fullerene carbon nanocages,like that described by Saunders et al., will likely benefit from thisstrategy as well. This involves insertion of neutral species withcorrespondingly larger radii. If the fullerene carbon nanocage is firstfluorinated, the insertion barrier (in this case involving the breakingand subsequent reformation of carbon-carbon cage bonds) should belowered on account of a reduction in the carbon-carbon bond strength ofthe cage. Thus, it is predicted that the species inserted under thistype of high-temperature/high-pressure doping will need to possess lesskinetic energy in order to achieve a successful penetration. Such ascenario would likely permit the employment of lower temperatures andpressures than were previously possible and result in higher yields.

[0232] While the theoretical calculations mentioned above for ioninsertion were done without breaking carbon-carbon cage bonds,fluorination of the cage exterior would likely permit endohedral dopingwith much larger species (ions or neutral species), assuming that thecarbon cage bonds do reform after species insertion. Thus, it isconceivable that fairly large ions could be inserted via bombardmentwith low-energy ions, and that fairly large neutral species could beinserted via high temperature/high pressure methods like in the case ofSaunders et al.

[0233] Endohedrally-doping fluorinated fullerene carbon nanocagestructures as described herein will facilitate the generation of aseries of new products of general type X@C_(m)F_(n), where X is one ormore endohedral doping species, that can be produced in industrialquantities. Such products will serve as nanoscale sources of radiationof different types (neutron, γ-rays, β-rays, α-particles etc.) formedical diagnostics, materials science, and in the production of otherhigh-technology products.

Example 4

[0234] 4.1 Endohedrally-Doped C₆₀

[0235] Step 1—Fluorination of a C₆₀ carbon nanostructure by aconventional procedure previously described [A. Gakh et al. “SelectiveSynthesis and Structure Determination of C₆₀F₄₈ ,” J. Am. Chem. Soc.,Vol. 116, p. 819 (1994)].

[0236] Step 2—Irradiation of the fluorinated carbon nanostructures witha T⁺ ion beam (ion-beam insertion into non-fluorinated fullerenes hasbeen described previously [R. Tellgmann et al. Nature Vol. 382, p. 407(1996)]. This procedure leads to the insertion of a chemical substanceinside the fluorinated C₆₀ carbon cage.

[0237] Step 3—(Optional) The fluorine can be removed by a reduction withhydrazine (or other appropriate reducing agent) [E. Mickelson et al.“Fluorination of Single Wall Carbon Nanotubes,” Chem. Phys. Lett., Vol.296, pp. 188-194 (1998)].

[0238] Step 4—(Optional) Surfactants can be used to protectcages-containers from chemical destruction, to ensure their solubilityand better biocompatibility, and to facilitate attachment ofbio-specific ligands [A. Hirsch “Functionalization of Single-WalledCarbon nanotubes,” Angew. Chem. Int. Ed., Vol. 41, No. 11, p. 1853(2002).

[0239] Step 5—(Optional) For biomedical targeting the surfactant can belabeled by specific antibodies as shown in FIG. 22 [K. Gonzalez et al.].

[0240] While the example provided describes using fluorination to lowerthe energy barrier for endohedral species insertion, other covalentlyattached atoms or functional groups (chlorine, hydrogen, hydroxyradicals, methyl groups, phenyl groups, etc.) may provide a similareffect. Furthermore, the fluorination may serve as a precursor step toalkyl functionalization, like that described previously [Boul et al.“Reversible Sidewall Functionalization of Buckytubes,” Chem. Phys.Lett., Vol. 310, p. 367 (1999).], whereby it is then thealkyl-derivatized fullerene carbon nanocage that is endohedrally-doped.Alternatively, this process may be carried out after the endohedraldoping.

[0241] Additional embodiments of the present invention utilize otherfullerene carbon nanocage species selected from the group consisting offullerenes, single wall carbon nanotubes, multiwall carbon nanotubes,nested fullerenes, buckyballs, bucky onions, carbon fibrils, andcombinations thereof. Methods of endohedrally inserting molecules,atoms, clusters of atoms, or ions into any of the these various types ofderivatized fullerene carbon nanocage species include ion implantationand high-temperature/high-pressure insertion. This may or may notinvolve the breaking and possible subsequent reformation of thecarbon-carbon bonds comprising the cage. The species so inserted may beany species capable of being delivered into and fitting into thefullerene carbon nanocage structure. The desired end-use may direct thechoice of the species with which to insert, and this may involve nucleitransmutation such that the desired product is actually a decay productof the species originally inserted. In all cases, the fluorine (orwhatever species is used to derivatize the fullerene carbon nanocage)may be removed after the endohedral doping process, and regardless ofwhether the fluorine (or other species) is removed, the exterior of theendohedrally-doped fullerene nanocage can be modified with a surfactantand/or antibodies for a variety of purposes, most notably medicinal.

[0242] This is a method for the efficient production of endohedralfullerene carbon nanocage species. This is accomplished by dramaticallydecreasing the potential barrier for penetration of ions, atoms, andmolecules into the interior of fullerene carbon nanocage species byfirst fluorinating the exterior carbon walls of the nanocage. This iseffected, in part, by a fundamental increase in the chemical stabilityof the carbon walls of endohedral complexes with ions and activechemical species, upon fluorination. Many markets will undoubtedlyemerge for such endohedrally-doped nanocages based on their increasedavailability, most notably in the pharmaceutical arena.

1. A method comprising the steps of: (a) covalently attaching species tothe exterior of the fullerene carbon nanocage to form a derivatizedfullerene carbon nanocage; and (b) inserting an endohedral doping agentinto the derivatized fullerene carbon nanocage.
 2. The method of claim1, wherein the derivatized fullerene carbon nanocage is a fluorinatedfullerene carbon nanocage.
 3. The method of claim 1, wherein the step ofcovalently attaching decreases the potential energy barrier for the stepof inserting.
 4. The method of claim 1, wherein the fullerene carbonnanocage is selected from the group consisting of fullerenes,buckyballs, carbon nanotubes, nested fullerenes, bucky onions,single-wall carbon nanotubes, multi-wall carbon nanotubes, carbonfibrils, and combinations thereof.
 5. The method of claim 1, wherein theendohedral doping agent is selected from the group consisting of acharged species, a neutral species, ion(s), atom(s), atom clusters,molecules, and combinations thereof.
 6. The method of claim 5, whereinthe endohedral doping agent is radioactive.
 7. The method of claim 5,wherein the endohedral doping agent is inserted via ion bombardment. 8.The method of claim 5, wherein the step of inserting comprises ahigh-temperature and high-pressure process.
 9. The method of claim 5,wherein the endohedral doping agent decays into a radioactive species.10. The method of claim 1, further comprising removing at least some ofthe covalently attached species from the exterior of the fullerenecarbon nanocage after the step of inserting.
 11. The method of claim 1,further comprising adding bio-specific ligands or antibodies to thefullerene nanocage.
 12. The method of claim 11, wherein the step ofadding occurs before the step of attaching.
 13. The method of claim 11,wherein the step of adding occurs during the step of attaching.
 14. Themethod of claim 11, wherein the step of adding occurs between the stepof attaching and the step of inserting.
 15. The method of claim 11,wherein the step of adding occurs after the step of inserting.
 16. Themethod of claim 1, wherein the step of inserting comprises breaking andsubsequent reformation of carbon-carbon bonds in the fullerene nanocagestructure.
 17. A method comprising: (a) derivatizing a fullerene; and(b) endohedrally modifying the fullerene.
 18. The method of claim 17,wherein the fullerene is a fullerene tube.
 19. The method of claim 18,wherein the fullerene tube is a single-wall carbon nanotube.
 20. Themethod of claim 19, wherein the sidewall carbon nanotube is derivatizedon the sidewall of the single-wall carbon nanotube.
 21. A compositioncomprising: (a) a fullerene; (b) a first species covalently attached tothe fullerene; and (c) a second species endohedrally located in thefullerene.
 22. The composition of claim 21, wherein the second speciesis selected from the group consisting of ions, atoms, molecules, andcombinations thereof.
 23. The composition of claim 21, wherein thesecond species is radioactive.
 24. The composition of claim 21 furthercomprising a third species attached to the fullerene, wherein the thirdspecies is selected from the group consisting of bio-specific ligands,antibodies, and combinations thereof.
 25. The composition of claim 21,wherein, the first species is selected from the group consisting ofbio-specific ligands and antibodies.
 26. A composition comprising: (a)fullerene carbon nanocage; (b) a first species covalently attached tothe fullerene carbon nanocage; and (c) a second species endohedrallylocated in the fullerene carbon nanocage.
 27. The composition of claim26, wherein the first species covalently attached to the fullerenecarbon nanocage is fluorine.
 28. The composition of claim 26 furthercomprising a third species attached to the fullerene, wherein the thirdspecies attached to the fullerene carbon nanocage is selected from thegroup consisting of bio-specific ligands, antibodies, and combinationsthereof.
 29. The composition of claim 26, wherein the second speciesendohedrally located in the fullerene carbon nanocage is a radioactivespecies.
 30. The composition of claim 29, wherein the radioactivespecies is selected from the group consisting of T⁺, T₂, ³He, cobaltisotopes of small ionic radius, and combinations thereof.
 31. The methodof claim 26, wherein the fullerene carbon nanocage is a fullerene tube.32. The method of claim 31, wherein the fullerene tube is a single-wallcarbon nanotube.
 33. The method of claim 32, wherein the sidewall carbonnanotube is derivatized on the sidewall of the single-wall carbonnanotube.